Ketchum algae treatment kills fish

The treatment to eliminate algae in Lake Ketchum didn’t go quite as planned, but Gene Williams said it will be OK in the long run.

“We had to stop treatment early because some little fish were dying,” said Williams, a senior planner for Snohomish County’s Surface Water Management (SWM) in the Department of Public Works…

“It was because of the timing and the weather,” he said. “We should have started a month earlier.”

Nonetheless, tests taken on June 10 showed 80 percent reduction of blue-green toxic algae.

Unseasonably dry, hot weather in early May caused more blooms and the lake warmed up sooner than usual. The algae blooms form a flock of snowflake like blossoms that sink at night, he explained.

That stressed the fish.

The contractor, Aqua Technex, from Bellingham, closed the boat launch four days in May to spray from a boat 20,400 gallons of alum and 11,300 gallons of sodium aluminate on the surface of Lake Ketchum.

The nontoxic acidic alum was mixed with the sodium aluminate to preserve the pH balance.

The mixture was expected to reduce the high level of phosphorus in Lake Ketchum by up to 85 percent with no lasting impacts to the lake or aquatic wildlife.

But the two liquids were not adequately mixed, Williams said.

“We saw peaks and valleys of pH.”

When some 3- to 5-inch yellow perch and a few trout were found dead, they stopped treatment.

Williams said they completed two-thirds of the treatment and will finish this fall, “probably November,” when temperatures drop again.

Toxic blue-green algae, or cyanobacteria, is a natural part of Northwest lakes, but sometimes it can grow rapidly or bloom. Lakes experiencing a bloom will look cloudy. When the algae accumulate as surface scum it resembles blue or green paint.

Some blue-green algae species produce toxins while blooming. Officials say that the algae does not affect the edibility of fish, although the fish should be washed thoroughly, but the persistent toxic blue-green algae at Ketchum has limited water activities during the past several years.

Lake Ketchum grows excessive algae because of high levels of nutrient pollution, particularly phosphorus, which feed the algae. Phosphorus levels are 13 times greater than regional standards and are some of the highest levels in the state.

Snohomish County conducted a study in 2010-2012 to find the main pollution sources in order to identify options for cleaning up the lake.

The main phosphorus sources include:

  1. An inlet that drains a former dairy farm is the source of 23 percent of the phosphorus. It is the original pollution source.
  2. Phosphorus pollution has built up in the lake sediments for decades and is now the largest source, at 73 percent.
  3. The remaining phosphorus, 4 percent, comes from rain, groundwater and other sources, such as septic systems, pet wastes and fertilizers.

The treatment was made possible by the local homeowners who agreed to help pay, and who helped write grants and seek funding, which they garnered from the Stillaguamish Clean Water District the state Department of Ecology and Snohomish County.

“The treatment is the first step toward preventing toxic algae blooms caused by phosphorus pollution and restoring water quality,” Williams said.

Following this initial treatment, annual treatments are planned for the next six or seven years. Williams said.

Information is available at, or call 425-388-3464.


Photo caption: Photo by SARAH ARNEY. Filamentous algae at the boat ramp of Lake Ketchum is not the same as the toxic blue-green algae blooms that were treated in May. Although the treatment was cut short, tests show an 80 percent reduction in the toxic blue-green algae.

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