Fish kill planned for West Medical Lake as WDFW responds to goldfish infestation impacting trout

If you’ve been to West Medical Lake, the sight of flashy goldfish in the shallows is not uncommon. Likely illegally introduced by pet owners or fisherman using live bait, the goldfish have out-competed the trout populations and are having devastating ecological impacts.

“There are times when they move up in the shallows and it looks like you can walk across their backs,” said Washington Department of Fish and Wildlife, Fish Biologist Randy Osborne, “its just a sea of orange.”

He says the goldfish have caused a population collapse of the trout, and given a few years there may be none left in the lake.

“If you are checking out anglers and all they are catching is big fish, that means that the little fish you stocked, they have tanked and died,” he said.

He says the decision has been made to now treat the lake with a chemical called rotenone.

“It disrupts the fishes ability to process oxygen, it doesn’t take the oxygen out of the water,” said Osborne.

The result, all the gill breathing organisms in the lake will die and after a few weeks the rotenone will degrade naturally.

He says health-wise the biggest concern is during application, as its a powder and inhalation is a risk. However, its applied through pipes and mixed with water, and its not likely to be a problem.

As for the wildlife, he says they won’t be impacted.

“The birds will really have a feast in the beginning,” he said.

The lake will be closed at the time of application, and folks shouldn’t collect the fish that have died.

Prior to the treatment, he says there will be a special trout fishing opportunity and folks will be able to take home as many trout as they can catch.

Clearing the lake completely is a cost effective solution, and Osborne explains can save the WDFW upwards of $2 million over the course of 10 years, because when restocking the lake, they can use smaller, younger trout fry that would otherwise be out-competed by the goldfish.

“The cost to raise a spring fry rainbow trout is about 4 cents a piece,” he said, “a catch-able size rainbow is about $1.51.”

West Medical Lake was last treated with rotenone nine years ago. A full treatment costs about $150,000.

Osborne says both Rainbow trout and Brown trout will be released this year. He hopes Brown trout, which are more piscivorous will be able to better handle any future goldfish introductions, and though they wouldn’t be able to solve the problem completely, they would likely extend the fishery life by three to four years.

Treatment will begin in October, with restocking to take place the following spring.