Experts say low oxygen, high temperatures caused fish ‘die off’

On the shores of Lone Lake, the small waves caused by the whipping wind have brought a smelly issue to the surrounding land: dead rainbow trout — lots of them.

The rotting fish, which number in the dozens in some areas of the shore, line the entirety of the lake. Concerned anglers, many who see Lone Lake as a prime spot for trout fishing, reported the situation to the state spurring an investigation. Officials from the Washington Department of Fish and Wildlife and the Washington State Department of Ecology visited the lake on Monday to determine the cause of the issue.

Justin Spinelli, fisheries biologist at the Washington Department of Fish and Wildlife (WDFW), estimated that roughly 1,000 dead trout were visible on the shore. That estimate doesn’t count fish that may be dead and floating in deeper areas of the lake. In his six years at the department, he says he has never seen anything this severe in the area.

“We’ve had this issue before, but I’ve never heard of anything that has been to this scale,” Kevin Lungren, president of the Fishin’ Club of Whidbey Island said. “It’s tragic this has happened. I don’t think there is anyone to blame, the state has managed it well.”

The issue initially caught WDFW’s attention when a lake user reported seeing “a strange plume” in the lake in addition to the large numbers of dead fish reported. The report brought Zach Gastin, lead spill responder for the Washington State Department of Ecology, to the investigation, but the two were quick to dispel the possibility of a toxic spill.

Spinelli said there are two primary causes for the fish “die off.” First, the lake has a low dissolved oxygen level of 1.3 milligrams per liter, whereas the normal level is 3.0. The fish were suffocating, and according to Whidbey Island Fly Fishing Club President Clayton Wright, they could be seen on the shore last week struggling for oxygen. Spinelli said the other cause of the die off is the “stressfully warm” temperatures the lake has seen throughout the summer. The average temperature of the lake on Monday was 65 degrees Fahrenheit, Spinelli said.

“It’s a fairly simple story,” Spinelli said. “We have a lake that’s not really stable and had been very warm, so water temperatures got high, dissolved oxygen got too low, and unfortunately fish got too stressed.” The lake has had vegetation and oxygen issues in the past, partly due to the lake’s shallowness. Lone Lake also doesn’t flush very well, as is the case with most western Washington lakes, according to Spinelli. Although this is a regular occurrence this time of year, the magnitude of the fish die off has South Whidbey fisherman concerned.

“The fish population declined last year, it was much better two years ago,” Clayton Wright, president of the Whidbey Island Fly Fishing Club said. “It probably will never be how it used to be. It’s’ not as consistent as it was two years ago.”

Anglers aren’t too worried about the rotting fish becoming a rank nuisance, though. It isn’t part of WDFW’s protocol to send a cleanup team, but Wright says nature will do its work.

“Between the ospreys and eagles, there won’t be fish out there for that much longer,” Wright said.