Reston Association treated Lake Audubon with a herbicide Tuesday in response to an infestation of hydrilla, an aquatic plant. The homeowners association is closing the lake, prohibiting fishing or boating, until this Friday, June 28.
Diana Saccone, Reston Association's watershed manager, said closing the lake is a precaution, and that the chemical should not have any lasting effect on the lake.
Hydrilla, an exotic plant, has been present at Lake Audubon for eight years. Now it has spread to over 80 percent of the lake and Saccone said it is growing one to three inches longer each day. She has heard several complaints from boaters and fishermen who have been frustrated by the weed.
"I've heard from people with broken boat propellers," Saccone said.
Reston Association carefully considered the ramifications before introducing the herbicide, Aquathol K, into the lake. Saccone said the homeowners association researched the available chemicals for years, speaking to several area lake mangers, before settling on Aquathol K. Endothall, the active ingredient in the herbicide, has a half life of just a day or two, Saccone said, and it breaks down into water and carbon dioxide.
"It's a contact killer," Saccone said. "It breaks down the plant when it touches it. There is no risk to waterfowl, other plants, or fish."
Enough chemical will be used to leave 20 percent hydrilla cover on the lake. Some of the plant will be left to provide oxygen and protection for the fish.
"You don't want to take away all the oxygen and have a fish kill," Saccone said.
Reston Association recently introduced 135 new plant-eating carp in the lake to limit hydrilla growth. Similar carp have lived in the lake for several years, but Saccone said they have not been able to keep up with the hydrilla.
Saccone said Reston Association staff will monitor the success of the treatment, and may conduct additional chemical treatments in the future.
BUT JAY FELDMAN, executive director of Beyond Pesticides, a national organization founded to prevent the misuse of pesticides, said long-term use of endothall may create a health risk. He said endothall may be necessary when hydrilla growth is out of control. But he said mechanical treatment, such as aquatic mowing, should be employed in the future so as not to develop a dependence on the chemical.
Saccone said the plant "grows by fragmentation," and that every time it is cut, it grows back even stronger.
"The weed's resistance means you are put on a treadmill," Feldman said. "Additional chemicals are needed over time as the plant develops a tolerance."
The Environmental Protection Agency has not completed a comprehensive study of the risks of endothall, so the long-term effects cannot be determined.
Bill Kirkpatrick, owner of Pennsylvania-based Aquatic Environment Consultants, recommended that Reston Association use endothall. He said the chemical is widely used to control hydrilla growth.
"There are water bodies that have been treated for 20 or 30 years with no adverse affects," Kirkpatrick said. "It doesn't bio-accumulate in the food chain. It just breaks down and it is gone, undetectable."
Hydrilla in the United States was first seen in Florida. It spread north by floating downstream, attaching itself to boats and fishing lures.