Hydrilla (wikimedia.org).

     VA.- In the 1990s when the Lake Anna Advisory Committee decided to bring in 6,200 sterile grass carp, the lake's hydrilla infestation had made many bays difficult to navigate. The carp, which were successful, mostly controlled the hydrilla while, unfortunately, eating a lot of the native vegetation as well. 

     However, as of this summer, hydrilla has returned, covering around 3 to 5 acre in the 13,000 acre lake. And the Advisory Committee decided they will not wait for the hydrilla to become a problem; spot herbicide treatments will probably be done in late August to curb the infestation before it gets out of control.