Once a colony of zebra mussels is established in a body of water, it is nearly impossible to prevent them from spreading elsewhere KEEP + ( ) OUT Boats, motors and trailers should be allowed to dry thoroughly in the sun for at least five days before boating again to ensure extermination Ma* Werner All they have done is filter out all the algae which normally would be food for native microscopic organisms. Great Lakes officials estimate that as much as $5 billion will be spent in 10 years on zebra mussel control.