Riparian Association Control Strategy Assessment …nstlra.com/Downloads/2015EWM_control_report.pdfNorth & South Twin Lakes 2015 AIS Monitoring & Riparian Association Control Strategy

North & South Twin Lakes 2015 AIS Monitoring & Riparian Association Control Strategy Assessment Report

January 2016 1

INTRODUCTION

North and South Twin Lakes, Vilas County, are approximate 2,788- and 642-acre drainage lakes, respectively (Photo 1). North Twin Lake flows into South Twin Lake, and South Twin Lake is drained via the Twin River. Eurasian water milfoil (Myriophyllum spicatum; EWM) was first documented in this system in 2001 and has been actively managed (hand-harvesting and herbicide treatment) since. The 2015 control plan included professional hand-harvesting in North Twin Lake and only EWM population monitoring of South Twin Lake. This was based on EWM population increases observed in South Twin Lake during recent years that make it impossible for hand-harvesting to provide population-level benefits to the lake. The EWM population of North Twin Lake is more contained and potentially a better candidate for this control method. MONITORING METHODOLOGIES

A set of EWM mapping surveys were used within this project to coordinate and qualitatively monitor the hand-harvesting efforts. A 2014 late summer EWM peak biomass survey was conducted and served as a pre-hand harvesting survey. Based upon this survey, a control strategy was formulated over the winter of 2014/2015, including the creation of prioritized hand-harvest areas. The control strategy implemented during the summer of 2015. After the hand-harvesting operations ceased, a Late-Summer EWM Peak-Biomass Survey was conducted in 2015 serving as a post-hand-harvesting assessment. To be considered successful, the population size and/or density of EWM within the hand-removal areas would need to decrease from the 2014 Late-Summer Peak-Biomass Survey (pre) to the 2015 Late-Summer Peak-Biomass Survey (post). 2014 EWM SURVEY RESULTS (PRE-HAND-HARVESTING)

On August 26 and 27, 2014, Onterra ecologists conducted the Late-Summer Peak-Biomass survey on North and South Twin Lake. During the survey, the EWM population was mapped using sub-meter GPS technology by using either 1) point-based or 2) area-based methodologies. Large colonies >40 feet in diameter are mapped using polygons (areas) and were qualitatively attributed a density rating based upon a five-tiered scale from Highly Scattered to Surface Matting. Point-based techniques were applied to EWM locations that were considered as Small Plant Colonies (<40 feet in diameter), Clumps of Plants, or Single or Few Plants. Onterra recommended that professional hand-harvesting efforts be directed at EWM locations identified in North Twin Lake during the late-summer of 2014, with a priority of targeting newly located occurrences furthest from the inlet to South Twin Lake (Map 1). Onterra provided the spatial data from this survey to the NSTRLA and the professional hand harvesting firm to direct the control efforts.

Photo 1. North & South Twin Lakes, Vilas County.


January 2016 2

HAND-HARVESTING MANAGEMENT ACTIONS

The NSTLRA contracted with Aquatic Plant Management, LLC to conduct professional hand-harvesting of EWM in 2015. Aquatic Plant Management, LLC conducted hand-harvesting activities throughout the summer of 2015, spending a combined 324.55 hours on the lake (approximately 184.5 hours underwater) removing approximately 650 cubic feet or 9,700 pounds of EWM. The hand-removal efforts conducted in 2015 were concentrated on sites C-15 and D-15 near the island on the southern end of North Twin Lake (Map 1). Approximately 455 cubic feet of EWM was removed from site C-15 over the course of 133.75 hours and another 196 cubic feet was removed from D-15 over the course of a combined 50.75 hours (Table 1). No hand removal efforts were conducted in sites A-15, B-15 or E-15, despite being prioritized for removal per Onterra’s recommendation. Details of the hand removal efforts during 2015 on North Twin Lake as reported by APM are included as an appendix to this report (Appendix A).

Table 1. North Twin Lake, 2015 professional hand-harvesting activities

Site C-15 Site D-15

Date SiteNumber of

Divers

Combined Dive Time

(Hours)

EWM Removed

(Cubic Feet)

7/8/2015 C-15 3 7.50 36.1

7/12/2015 C-15 3 6.75 28.2

7/13/2015 C-15 3 7.25 36.8

7/14/2015 C-15 3 7.75 32.2

7/16/2015 C-15 3 6.00 23.8

7/20/2015 C-15 3 5.25 22.8

7/21/2015 C-15 3 7.50 34.8

7/23/2015 C-15 3 5.25 21.0

7/24/2015 C-15 3 6.75 21.8

7/27/2015 C-15 3 12.25 49.9

7/28/2015 C-15 3 7.50 18.8

7/29/2015 C-15 4 7.00 5.3

7/30/2015 C-15 4 10.00 14.5

8/3/2015 C-15 6 13.50 41.0

8/4/2015 C-15 3 7.75 16.6

8/5/2015 C-15 3 9.75 25.7

8/6/2015 C-15 3 6.00 25.8

Total 133.75 455.1

Date SiteNumber of

Divers

Combined Dive Time

(Hours)

EWM Removed

(Cubic Feet)

7/7/2015 D-15 3 7.75 35.6

7/9/2015 D-15 3 8.25 37.2

7/17/2015 D-15 3 6.00 24.0

7/20/2015 D-15 3 5.25 25.3

7/22/2015 D-15 3 11.00 32.8

7/23/2015 D-15 3 4.50 12.4

7/31/2015 D-15 4 8.00 29.1

Total 50.75 196.4


January 2016 3

2015 EWM SURVEY RESULTS

The Late-Summer EWM Peak-Biomass Survey was conducted on September 16-18, 2015 to qualitatively assess the hand harvesting efforts as well as to understand the peak growth (peak-biomass) of the EWM population throughout the vegetated areas of the lake. Post Hand-Harvesting

APM removed approximately 455 cubic feet of EWM from within and around site C-15 (Table 1). The post hand harvesting survey shows that a dominant EWM colony remains in the site and the site is relatively unchanged or slighlty more dense than compared to 2014 (Figure 2). Approximately 196.4 cubic feet of EWM was reportedly removed from site D-15 by APM in 2015. The post hand harvesting survey shows little improvement within the site compared to 2014 levels with large dominant, highly dominant and surface matting colonies of EWM remaining present in the site (Figure 2). This indicates that while a great deal of EWM biomass was removed during the 2015 hand-harvesting efforts, the efforts were not sufficient to overcome the overall population increase within the targeted areas within North Twin Lake. Expansion of the EWM colonies outside of the targeted hand harvest sites was also observed, notably westward from site C-15 as well as along the west edge of the nearby island (Figure 2).

Figure 2. August 2014 Pre- and September 2015 Post-Professional Hand-harvesting Locations on North Twin Lake.


January 2016 4

North Twin Lake

Please note that the following figures (Figures 3-4) represent the acreage of mapped EWM polygons, not EWM mapped within point-based methodologies (Single or Few Plants, Clumps of Plants, or Small Plant Colonies). Taken out of context, this figure can be misleading as it relates to the EWM population changes. For instance, large increases in colonized acreage may seem like drastic changes, but actually represent when a collection of point-based EWM occurrences increase in density to the point they require delineation with polygons. Within North Twin Lake, colonized EWM acreage estimates remained approximately the same between 2014 to 2015 at roughly 6.5 to 7 acres. However, a greater proportion of the 2015 colonial acreage is comprised of dominant or greater density ratings than in 2014. This suggests that while the size of the EWM population within North Twin Lake may not have noticeably increased, the EWM densities increased during this time period. Several additional EWM occurrences were located within other locations of North Twin Lake during 2015 (Map 2). South Twin Lake

In 2010, a large-scale herbicide treatment was conducted on South Twin Lake that resulted in no EWM being located in 2010 (Figure 4). A low population level, mostly comprised of point-based EWM occurrences was observed in 2011 and 2012. In recent years, the EWM population of South Twin Lake has increased in coverage and density to levels observed prior to large-scale management (Map 3) Nearly every summer since 2008, a point-intercept survey has been completed on South Twin Lake by either WDNR or Onterra staff. A substantial decrease in EWM frequency of occurrence occurred following the whole-lake treatments conducted during the spring of 2009 and spring of 2010 (Figure 5). During the summer of the 2010 treatment, EWM was not detected during the point-intercept survey and was only located at one sampling location in 2011. EWM had begun to show signs of rebound during the 2013 and 2014 surveys, however remained similar to or below levels observed in 2009 prior to the whole-lake treatment. In 2015 the littoral frequency of occurrence of EWM increased significantly compared to 2014, and at 37.7%, is higher than any survey since data collection began in 2008 (Figure 5).

Figure 3. Acreage of mapped EWM colonies on North Twin Lake from 2010-2015.

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January 2016 5

Eurasian water milfoil (Myriophyllum spicatum)

Figure 4. Acreage of mapped EWM colonies on South Twin Lake from 2010-2015.

Figure 5. Littoral occurrence of EWM from South Twin Lake from 2008-2015. Open circle represents a statistically valid change in occurrence from previous survey (Chi-square α = 0.05).

Figure 6 highlights eight of the nine native aquatic plant species that showed initial declines following the 2009 and 2010 whole-lake 2,4-D treatments. Northern water milfoil and water marigold are both dicot species that had populations reduced to near zero following the set of whole-lake treatments. Slow recovery has been observed from both species with frequencies observed in 2015 similar to 2009 levels, but somewhat below 2008 levels. The slender naiad population in South Twin Lake experienced a decline in its occurrence following the 2010 whole-lake 2,4-D treatment, and was found to have rebounded to above pretreatment occurrences in 2011. Slender naiad relies heavily on annual seed production for reproduction, and data from other whole-lake treatments shows a similar population trend. Variability in this species’ population has been observed in recent years on South Twin Lake. Similarly, common waterweed initially declined during the summer of the 2010 treatment but rebounded to above pretreatment levels in 2011. Variable leaf pondweed and water stargrass have shown a full recovery since the 2010 whole-lake treatment. Flat stem-pondweed and small pondweed both rebounded to near pretreatment levels by 2013 before showing a downward population trend in the last two years despite no management actions. Populations of a few species may show declining trends in recent years, potentially as other plant species (native and non-native) increase in occurrence and compete for space.

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2010 2011 2012 2013 2014 2015

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January 2016 6

Northern water milfoil (Myriophyllum sibiricum) Water marigold (Bidens beckii)

Common waterweed (Elodea canadensis) Slender naiad (Najas flexilis)

Variable leaf pondweed (Potamogeton gramineus) Flat-stem pondweed (Potamogeton zosteriformis)

Water stargrass (Heteranthera dubia) Small pondweed (Potamogeton pusillus)

Figure 6. Littoral occurrence of species that initially declined following whole-lake treatments on South Twin Lake. Created using data from WDNR 2008, 2013-14 and Onterra 2009-11 & 2015 point-intercept surveys. Open circle represents a statistically valid change in occurrence from previous survey (Chi-square α = 0.05).

28.3

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2008 2009 2010 2011 2012 2013 2014 2015

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18.413.2

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January 2016 7

Figure 7 highlights six native species that were largely unaffected by the 2009 and 2010 whole-lake treatments on South Twin Lake. Small fluctuations have been observed annually, none of which likely resulted from the herbicide control strategy.

Coontail (Ceratophyllum demersum) Wild celery (Vallisneria americana)

Fern pondweed (Potamogeton robbinsii) Muskgrasses (Chara spp.)

Clasping-leaf pondweed (Potamogeton richardsonii) White-stem pondweed (Potamogeton praelongus)

Figure 7. Littoral occurrence of species that were not statistically impacted by whole-lake treatments on South Twin Lake. Created using data from WDNR 2008, 2013-14 and Onterra 2009-11 & 2015 point-intercept surveys. Open circle represents a statistically valid change in occurrence from previous survey (Chi-square α = 0.05).

23.4 22.0 21.0 22.0

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10.5 10.5 10.47.6

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January 2016 8

CONCLUSIONS AND DISCUSSION

Overall, the 2015 professional hand-harvesting on North Twin Lake did not reduce or maintain the level of EWM in the targeted areas. The EWM was found to have expanded over the course of the summer faster than what efforts to remove it could accomplish. Although hand harvesting efforts fell short of control expectations, the removal efforts in these sites may have slowed the overall expansion of EWM in the targeted areas. Lake wide, North Twin Lake EWM levels are still relatively low with the majority of known EWM concentrated in the southern portion of the lake nearest to South Twin. Hand removal efforts in North and South Twin Lakes over the past several years have struggled to make a noticeable difference in the areas targeted. Map 2 outlines hand-harvesting areas in North Twin Lake where professional hand-harvesting efforts should provide effective control in 2016. The EWM within these locations is low in density and may be considered pioneering populations within these parts of the lake. Other EWM colonies in North Twin Lake, specifically those in the southwestern part of the lake between the island and South Twin Lake (Map 2) are believed to exceed the size and/or density levels that can be effectively controlled with hand-harvesting methods. If the NSTLRA would like to target these locations for control, it is recommended to conduct spot treatments with herbicides that require short exposure times, such as diquat or herbicide combinations (diquat/endothall, 2,4-D/endothall, etc). It is recommended to focus the planning and monitoring of this type of treatment during the year following large-scale efforts that may take place on South Twin Lake. A significant increase in EWM acreage and density was observed throughout South Twin Lake, now exceeding levels from prior to the 2009-2010 whole-lake herbicide treatments. The dense and noticeable EWM population in South Twin Lake raised concerns from NSTLRA members (Photo 2), spurring a meeting between Eddie Heath of Onterra and board members of the NSTLRA in early summer. At that time, a discussion about conducting another whole-lake herbicide treatment on the lake occurred. Later that summer, the NSTLRA held another meeting, this time also inviting Kevin Gauthier, WDNR Regional Lakes Coordinator to the meeting. A healthy discussion of control strategies, EWM population dynamics, and lake management planning took place. During December 2015, the NSTLRA applied for a WDNR grant to update their Comprehensive Lake Management Plan. Their previous plan was finalized in August 2006 and has aspects that may be slightly outdated. However, the Aquatic Plant Section was updated during February 2012 as a part of a final evaluation for a multi-year AIS-EPC Grant and the AIS Control Strategy has been updated annually through a formal AIS Monitoring Report.

Photo 2. Matted EWM on South Twin Lake. August 2015.


January 2016 9

The NSTLRA also voted to move forward with a whole-lake herbicide treatment for South Twin Lake during the spring of 2016. The EWM population in South Twin Lake is comprised of confirmed pure-strain EWM plants and is suspected as being classically susceptible to a whole-lake 2,4-D treatment. For this reason, a whole-lake 2,4-D treatment is being proposed for 2016. That being said, it is generally recommended to rotate herbicide use strategies to minimize an evolved herbicide tolerance (resistance) of the target population. Within any genetically diverse plant population, there are likely some individuals that naturally have a higher tolerance to herbicides due to random genetic variations. The repeated use of the same herbicide may select for and create an EWM population that is now more resistant to the herbicides that were utilized, where typical use patterns of the herbicide are not as effective. Herbicide resistance is suspected of taking place in Wisconsin lakes that have been actively targeting hybrid water milfoil (sexual cross between EWM and northern water milfoil [Myriophyllum sibiricum]) consecutively with large-scale 2,4-D management. However, no evidence currently exists about evolved herbicide tolerance from a pure-strain EWM population. To have more certainty whether South Twin’s invasive milfoil population consists of herbicide-tolerant strains, NSTLRA partnered with SePRO to conduct laboratory studies termed “challenge testing” on a subset of plants from the lake. As a company that produces aquatic and terrestrial herbicides, SePRO has developed baseline challenge testing procedures (PlanTEST®) using the herbicide products they manufacture (2,4-D – Sculpin®, triclopyr – Renovate®, and fluridone – Sonar®). In the late summer of 2015, Onterra staff collected over 150 EWM plant meristems from three locations and sent them to the SePRO Research and Technology Campus for herbicide challenge testing that is currently underway. If the challenge testing shows that the EWM plants in South Twin Lake show a reduced susceptibility to 2,4-D, other herbicide use patterns less commonly employed in northern Wisconsin may need to be given consideration. Having an extensive base of data from the 2009 and 2010 whole-lake treatments on South Twin Lake allows for a better understanding of expected efficacy and potential impacts to the native plant community at known 2,4-D concentrations from the past treatments. Map 4 displays the preliminary whole-lake 2,4-D herbicide treatment strategy for South Twin Lake. Advanced water volume calculations are displayed on the table embedded within the map, modeled using data from the 2010-2015 point-intercept surveys. The proposed 2016 target concentration of 0.35 ppm ae falls towards the higher end of the current whole lake treatment focus area where the balance of EWM control versus native plant impacts are thought to be more acceptable than what occurred in 2010. During 2016 (year of the treatment), a Pretreatment Verification and Refinement Survey would occur during the spring prior to the whole-lake treatment. This survey would potentially (but not likely) result in refinements of herbicide application areas, assessments of growth stage of aquatic plants, and documentation of thermal stratification parameters that will ultimately influence the final dosing strategy. Volunteer-based monitoring of temperature profiles would be coordinated surrounding the treatment, as well as collection of post treatment herbicide concentration samples at multiple locations and sampling intervals. During the year of treatment (2016) and year after treatment (2017), post treatment assessments would be made through replication point-intercept surveys and EWM mapping assessments. The NSTLRA understand that EWM population rebound is inevitable at some point following a whole-lake treatment. Depending on the results of the 2017 (year after treatment) surveys, NSTLRA would develop a long-term EWM control strategy based upon the lessons learned during this period, that may include strategic herbicide spot treatments or postponing active management until a replicate whole-lake treatment is warranted.


January 2016 10

The distribution of this document will ultimately spur additional conversations with project partners. Further examination of these data and resulting discussions will lead to developing an herbicide use pattern to adopt for 2016 as well as an AIS-Established Population Control Grant which will be applied for on February 1, 2016.

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Bathymetry (ft)0 - 22 - 44 - 66 - 108 - 1010 - 1212 - 1414 - 1616 - 1818 - 2020 - 2222 - 2424 - 2626 - 2828 - 3030 - 3232 - 3434 - 3636 - 3838 - 4040+ Deep

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Vilas County, WisconsinSouth Twin Lake

Proposed 2016 EWMControl Strategy

Map 4

Site AcresAve. Depth

(feet)Volume(ac-ft)

2,4-DPPM ae

DMA IV(gallons)

A-16 161.25 7.5 1209.4 2.30 1990

0.351 ppm ae - Target calculated epilimentic (18ft) 2,4-D concentration

Preliminary 2016 EWM Control StrategyLiquid 2,4-D

1696 Silver Beach Drive Lac du Flambeau, WI 54538

North Twin Lake EWM Removal Report Summer 2015

Aquatic Plant Management LLC

North Twin Lake EWM Removal Summary 2015

Summary: During the month of July and the first week of August, 2015 Aquatic Plant Management LLC (APM) conducted hand harvesting services of Eurasian Water Milfoil (EWM) on North Twin Lake. Our experienced divers spent a combined total of 324.55 hours on the water and were able to successfully remove approximately 650 cubic feet or 9,700 pounds of EWM from the lake.

Dive Conditions: Conditions on North Twin for the duration of APM’s hand-harvesting efforts were generally good, with the exception of 7/29/15 when very high winds limited our diving capabilities. Water clarity on North Twin was very good, with underwater visibility ranging from 8-10 feet. The relatively soft sandy substrate allowed for near complete removal of EWM root systems, further decreasing the likelihood of regrowth in the areas targeted.

Recommendations: The EWM infestation on North Twin lake is particularly established. In our experience it is one of the most high risk lakes that we have harvested on due to a combination of water clarity, limited growth of native plants, and close proximity to South Twin Lake’s large and highly dominant EWM beds. The North and South Twin Lakes Riparian Association has done a commendable job of recognizing the problem and mobilizing against it. Going forward we recommend that the Association continue to invest in both EWM monitoring and hand harvesting efforts to limit the expansion of the infestation. APM will be adopting more advanced methods of hand harvesting including, but not limited to, suction harvesting and hookah based diving. We believe that North Twin lake is the perfect candidate to use these methods to combat the spread of the infestation and promote the growth of native plant communities. North Twin Lake is our highest priority for EWM management for 2016.

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Detailed Summary of Diving Activities

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Date Latitude Longitude

Time Underwater (Min)

Estimated EWM Removed (Cubic Feet)

EWM Density Rating Comments

7/7/15 46.03861 89.15139 60 13.6 10 Sandy substrate. EWM was standing tall in the water column, with plants reaching lengths of 7-9 feet, causing some surface matting to occur. The substrate was sandy, but not so dense that root ball removal was impeded.





EWM Density Rating 0 1 2 3 4 5 6 7 8 9 10

Plants per 5 Square Yards 0 1-2 3-4 5-6 7-8 9-10 11-12 13-14 15-16 17-18 19-20



3














4





7/12/15 46.03917 89.15694 45 10.0 10 Sandy substrate. EWM was located in dense colonies, with individual plants spread out between them. Able to completely remove root systems

7/12/15 46.03917 89.15694 30 6.3 10 Sandy substrate. EWM was located in dense colonies, with indivual plants spread out between them. Plants were between 7-8 feet long, located in 8-10 feet of water.








5








7/16/15 46.03917 89.15694 60 13.1 8 Sandy substrate. EWM was located in dense clumps, with a few small colonies in the area. Plants ranged in length from 6-8 feet, and were located in 8-10 feet of water.






6





7/17/15 46.03861 89.15139 60 13.6 9 Sandy substrate. There were a few occurences of surface matting, but the majority of the EWM was located in dense clumps of plants in 8-10 feet of water.




7/20/15 46.03833 89.15833 45 10.4 9 Sandy substrate. EWM was located in dense clumps, with tall, individual plants spread throughout the area. Plants were located in 8-11 feet of water.





7





7/20/15 46.03833 89.15833 60 12.4 9 Sandy substrate. EWM was located in dense clumps, with tall, individual plants spread throughout the area. Plants were located in 8-11 feet of water.









8








7/23/15 46.03833 89.15611 60 11.9 8 Sandy substrate. EWM was located in clumps of 10-15 plants (6-8 feet tall) with scattered shorter (5-7 foot) plants in the area. EWM was found at a depth of 8-12 feet

7/23/15 46.03833 89.15611 45 9.1 8 Sandy substrate. EWM was located in clumps of 10-15 plants (6-8 feet tall) with scattered shorter (5-7 foot) plants in the area. EWM was found at a depth of 8-12 feet





9





7/23/15 46.03861 89.15139 30 4.8 8 Sandy substrate. Fewer occurences of surface matting, but a few areas were still present. Most EWM was located in dense clumps. Plants were found in 8-10 feet of water

7/23/15 46.03861 89.15139 60 7.6 8 Sandy substrate. Fewer occurences of surface matting, but a few areas were still present. Most EWM was located in dense clumps. Plants were found in 8-10 feet of water

7/24/15 46.03833 89.15833 45 6.7 8 Sandy substrate. EWM was located in small clumps of plants, surrounded by scattered individual plants ranging in height from 5-7 feet. Plants were found at a depth of 8-11 feet.







10














11





7/30/15 46.03917 89.15694 65 6.4 6 Sandy substrate. EWM was located in dense clumps, with a two small colonies in the area. Plants ranged in length from 6-8 feet, and were located in 8-10 feet of water.



7/31/15 46.03861 89.15222 30 9.1 7 Sandy substrate. EWM consisted mainly of large (6-8 foot) individual plants spread throughout the area. Most EWM plants were located in 7-10 feet of water.






12














13














14






8/6/15 46.03833 89.15833 60 11.6 5 Sandy substrate. EWM growth consisted mainly of scattered individual plants ranging in height from 5-7 feet. EWM was located in 8-9 feet of water






EWM Picture

15


Map Created by Onterra LLC

16

Riparian Association Control Strategy Assessment …nstlra.com/Downloads/2015EWM_control_report.pdfNorth & South Twin Lakes 2015 AIS Monitoring & Riparian Association Control Strategy

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