Down in the weeds: Efforts to control lake vegetation may have to be rescheduled

MOSES LAKE — Every June, the Moses Lake Irrigation and Rehabilitation District spends a few weeks spraying “noxious and invasive” aquatic weeds that grow in Moses Lake.

But they may not be able to do that this year.

According to Terry McNabb, owner of Bellingham-based Aquatechnex, a company that has assisted the MLIRD with lake treatments for weeds and algae for the last few years, a change in how the Department of Fish and Wildlife oversees the permit for herbicide treatments of Moses Lake could restrict weed control attempts to the fall and early winter — when the lake’s levels are low and plants begin to go dormant.

“Control efforts need to happen,” McNabb said during an online meeting Tuesday morning of the Moses Lake Watershed Council. “This affects the ability to deal with invasive aquatic plants.”

McNabb said the weed treatments, which are typically applied to roughly 2% to 3% of the shoreline and littoral areas of the lake beginning in mid-June, are an important part of maintaining the quality of the lake water and play a small role in containing the algae blooms that have plagued the lake in the last few years.

However, the Department of Fish and Wildlife has limited the use of aquatic herbicides to Aug. 31 through Dec. 31. According to the WDFW Habitat Program: Restricted Areas for Aquatic Herbicides website, the limits are needed to protect rainbow trout, walleye, the American white pelican, Clark’s grebe, long-billed curlew, tundra swan, Western grebe, common loon and concentrations of shorebirds and waterfowl.

“We’re trying to figure out what the scientific basis is for this timing window,” McNabb said. “I’m not even sure some of those species are present in Moses Lake.”

“The treatment timing windows have been in place for years,” Shawn Ultican, a general permit writer for the Department of Ecology, told participants in the online meeting.

WDFW oversees the aquatic herbicide treatment restrictions as part of an overall aquatic plant and algae management permit program, which are issued every five years by the Department of Ecology and were originally designed to protect endangered fish species like salmon. The MLIRD’s new aquatic weed management permit was renewed in March 2021, McNabb said.

Ultican said permit holders — in this case, the MLIRD — can apply for modifications to the permit, allowing them to apply the herbicide outside the permitted “treatment window,” something Aquatechnex has done on the irrigation district’s behalf.

“There’s been no delay in processing that request,” Ultican said.

After the meeting, McNabb said under the prior permit issued in 2016, his company received permission from WDFW to apply the herbicides to Moses Lake in June, and simply continued to do so.

“By law, permits issued are not to burden weed control efforts,” he said.

If the MLIRD has to wait until fall and early winter to apply the herbicides, weeds will spread more widely in the summer. And they may not work in the fall when aquatic plants also go dormant as the weather gets cold.

Most of the aquatic plants native to Moses Lake are grasses, McNabb said, while many of the invasive species are more broadleaf plants with herbicides especially designed to target them.

Ron Sawyer, owner of Cascade Marina and a member of the Watershed Council, said it might also behoove the MLIRD to encourage the growth of native plant species to have the local plants out-compete the invaders.

“That’s an alternative to using chemicals to kill every weed,” he said.

Charles H. Featherstone can be reached at cfeatherstone@columbiabasinherald.com.