Hydrilla considered eradicated in two King County lakes after lengthy battle

A 15-year battle to eradicate an invasive exotic water plant in two King County lakes may have been won. King County and state environmental managers are happy to report that extensive surveys of Pipe and Lucerne lakes this year turned up no sign of hydrilla.

It wasn’t long ago when King County faced a significant hydrilla infestation, even after many years of treatment.

In 2003, surveyors found 470 hydrilla plants in the two lakes, which are connected and are the only two water bodies in Washington known to have hosted the invasive plant.

Management and survey programs implemented by the county in recent years have shown remarkable results.

This marks the third year that none of the fast-growing invasive plants were found in Pipe Lake, and it’s the fifth year that Lucerne Lake has come up hydrilla-free after survey work, which allows managers to declare that the nasty aquatic plant has been eradicated and to stop treatment of the lakes with herbicides to combat the infestation.

“Some states spend millions of dollars every year to address hydrilla infestations in their waterways, so we are very lucky to be able to declare hydrilla eradicated from these two lakes and prevent its spread to other water bodies,” said Sally Abella, Lake and Streams team lead for the King County Department of Natural Resources and Parks’ Water and Land Resources Division.

Native to the warmer areas of Asia and first discovered in waters of the United States in 1960, hydrilla has caused numerous environmental problems in lakes and rivers – particularly in the Southeastern U.S. In the past, hydrilla was frequently sold as an aquarium plant, but has been banned in Washington state for a number of years.

It’s thought that most hydrilla infestations begin either when aquarium owners release their contents into lakes or rivers or when water lilies imported from states with hydrilla infestations are planted. Hydrilla can also be introduced to a new body of water by boats and trailers, as only small fragments of the plant are needed to start a new infestation.

Abella said the success of this hydrilla project is due in large part to the partnership forged between King County, the Washington Department of Ecology and the cities of Maple Valley and Covington.

The cities and state agency have provided funding for the program, while since 2003 King County has performed both herbicide treatments and monitoring, with the help of Herrera Environmental Consultants providing diver support.

Next year will be the first year in 14 years that herbicide will not be applied to either lake. This is great news for the lakes, as the native plant species should now colonize the lake, providing better fish habitat and ecosystem diversity.

Abella said King County will remain vigilant for signs of a return of hydrilla in the two lakes. Dive surveys will be done for at least the next three years to check for new plants.

More information on the hydrilla eradication program is available online at http://www.kingcounty.gov/environment/waterandland/lakes/plants/weed-identification/hydrilla/eradication-project.aspx.

Related information

Lakes of King County, Washington

Weed volunteer information

Aquatic weed identification

Hydrilla eradication project