ELLENSBURG – Signs will be posted at Mattoon Lake in Kittitas County advising swimmers to avoid going in the water June 8-9 when the lake will be treated with herbicide to control aquatic weeds.
The Washington Department of Fish and Wildlife (WDFW) plans to treat the 26-acre lake in Ellensburg with 2-4-D herbicide to control submerged Eurasian water milfoil, said David Heimer, noxious weed coordinator for the department.
Heimer said the permit approved by the Washington Department of Ecology for application of 2-4-D includes a 24-hour no-swimming advisory.
“This herbicide degrades rapidly, but treated water should not be used for irrigation or potable uses until concentrations diminish,” Heimer said. “We’ll be sampling the water regularly after application to determine concentrations.”
No other restrictions apply, so fishing in the lake will not be affected, Heimer said. The lake will reopen for swimming June 10.
WDFW will also treat the shoreline of Mattoon Lake and the shorelines of North and South Fio Rito lakes June 8-9 with imazapyr herbicide to control yellow flag iris. No restrictions or advisories are needed for that work, Heimer said.
The Fio Rito lakes, three miles southeast of Ellensburg, were treated for milfoil last summer, but Heimer will snorkel and use an underwater camera to check for any missed milfoil. Any re-treatment needed would be conducted later in June with advanced public notice.
Yellow flag iris and Eurasian water milfoil are both invasive, non-native plants that will choke out native habitat for fish and wildlife if allowed to spread, he said.
The work to improve the quality of the lakes is a cooperative project of WDFW, the Kittitas Noxious Weed Control Board, Washington departments of Agriculture and Ecology, and the Kittitas Field and Stream Club.