The city of Bellevue, Wash., closed two public beaches to swimming Monday as it sprayed herbicide into Lake Washington’s Meydenbauer Bay. It plans to close a third beach on Wednesday.
Bellevue is fighting an invasive weed known as Eurasian watermilfoil.
The city’s parks department planned to reopen the waters of Meydenbauer Beach and Clyde Beach to swimming Tuesday morning. The city plans to open Newcastle Beach Park to swimming Thursday morning after a 24-hour closure.
The Eurasian plant was first spotted in Lake Washington in the 1970s, and Bellevue has been fighting it for years.
“You can pretty much find it just about everywhere in the lake," said Rick Bailey of the Bellevue parks department. "If it’s left uncontrolled, it can actually, depending on the size of the lake, it can take over an entire lake within two years.”
City, county and state agencies across Washington state, as well as homeowners' associations and other private groups, spend up to $1 million a year to control milfoil, according to the Washington Department of Ecology. After decades of effort, they’ve reached a stalemate at best. Agencies no longer hope to eradicate milfoil — merely prevent it from spreading to new areas.
Individual strands of Eurasian watermilfoil appear feathery and delicate as they stretch toward the surface. But together, they form thick mats that can crowd out other species. The mats can also block a lake’s circulation and deplete the oxygen available to fish and other creatures.
“It’s probably the worst invasive noxious weed in Washington,” Bailey said.
Milfoil often gets stuck to boat propellers. Boaters can, knowingly or unknowingly, give it a free ride — especially when they launch into a different lake or river. Transporting any aquatic hitchhikers is illegal in Washington state. Even a tiny fragment of a milfoil strand can grow into a whole new plant.
The herbicide that Bellevue is using, Diquat, is less toxic than some others. It only kills the parts of plants it directly touches. Diquat doesn’t kill a plant's roots, unlike more powerful herbicides. So, to combat milfoil, Bellevue officials keep applying the herbicide every year or so near marinas and other infested areas.
Environmentalists don’t like milfoil, either, but some of them dislike herbicides more.
“We do have citizens who call in and complain about using pesticides in our parks,” Bailey said.
The city of Bellevue has tried other methods, including hiring divers to yank the weeds out by hand. Bailey said divers cost three to four times more than herbicides.
The Washington Toxics Coalition calls the repeated herbicide use in Bellevue and other areas of Lake Washington “chemical mowing.” The group says actual mowing with mechanical harvesters would be a safer way to keep milfoil from spreading, especially with young chinook salmon, a threatened species, migrating through the lake each summer.
You might be wondering why Bellevue would choose to close down its popular beaches in the middle of summer? According to Bailey, fewer salmon use Lake Washington in July and August than any other time of year, so late summer is the safest season to put herbicides in the lake.