Nine years after accidental fish kill, Wapato Lake to get algae treatment again

Nine years after a botched chemical treatment to get rid of algae at Wapato Lake massacred its fish, Metro Parks is preparing to try it again.

The 34-acre lake, in a pocket of South Tacoma surrounded by homes, highways and businesses, is prone to blooms of toxic blue-green algae. The Tacoma-Pierce County Health Department has raised alerts or closed the lake 10 times since 2013, by Metro Parks’ count, mostly in summer. When the weather warms this spring, the algae is expected to be not far behind, unless treatment is done in April or May.

Blame the landscape.

The lake originated as a “kettle” dug by the movement of ice-age glaciers. Streams don’t feed it. Rainwater that falls on the 900 or so acres around the lake flows downhill into Wapato. This is great for algae. The runoff carries in phosphorous from lawn fertilizer, pet and bird waste, and various bacteria, and a lake without tributaries has little agitation.

For people, this combination of factors leads to troubling conditions in a spot that has been a recreation area since the 1800s.

“It’s a great area for a park, but it’s got to have a significant amount of dollars to keep it as a lake over time,” said Brad Harp, the health department’s water resources manager.

In 2008, with conditions that made Wapato among the state’s most toxic lakes — and a danger to people and pets who splashed in it — Metro Parks tried remedying this by hiring a Minnesota-based contractor for $98,000 to put alum into Wapato. The alum binds with the phosphorous and settles on the water, which keeps algae on the surface from using the phosphorous as a nutrient.

It sounded good in planning. The company told The News Tribune its treatment would not harm people or animals. Then a supplier delivered the wrong mix of chemicals, tens of thousands of gallons of which were dumped into the lake from tanker trucks.

The good news: The waters got so clear from the death of the algae that detritus could be seen on the lake floor, including discarded bicycles and televisions, even an abandoned stolen car. All were hauled out of the water.

The bad news: The lake got so acidic from the treatment that hundreds of fish died.

A postmortem found that too much alum went in and too little of the buffer chemical to bring down the acidity was added.

“We had a bad, bad experience in 2008,” parks spokesman Michael Thompson said.

Parks officials eventually brought the lake’s acidity back to habitable levels, in part by buying 2,000 pounds of baking soda and adding that to the waters. Fish repopulated. On a recent sunny morning, mallards swam and dove for food vigorously.

This year, Metro Parks has hired a different company to handle the treatment, Seattle-based Herrera Environmental Consultants.

If it goes according to plan this time, the lake will be algae-free for five to eight years. Right away, if the plans work, the waters will clear up, and the fish will mostly survive.

“They’re basically going to monitor this very carefully,” Thompson said, “because everyone involved in this project is well aware of what happened in 2008. We do not want that to happen again.”

In part because of the attention the mishandled treatment got in 2008, Metro Parks is holding an informational forum at 6 p.m. Thursday at the Wapato Park Pavilion, 6500 S. Sheridan Ave.

The exact date of the treatment won’t be determined until two weeks before, Thompson said.

Other improvements at the lake are planned for the coming months, including building two docks for kayak launches and a fish-cleaning station.

“The goal is to improve the water so these docks have a purpose,” said Joey Furuto, Metro Parks community and neighborhood parks manager.

Parks officials expect algae treatments to become a regular every-few-years aspect of dealing with the lake. A longer-term fix is theoretically possible.

That would require much more extensive — and expensive — work, possibly including dredging the lake and changing the area’s drainage to keep the most phosphorous-rich runoff from reaching the waters.

One other unwanted consequence of the 2008 debacle might be trickier to avoid than simply keeping a close eye on chemical additives.

After the cleaning, the suddenly clear water attracted Canada geese in sharply increased flocks. Each goose can leave dozens of droppings per day.

This is a nuisance for human park users and a rich source of phosphorous and nitrogen, so when the goose feces washes into the water, it feeds the algae’s return.

For years, Metro Parks hired a patrol of dogs for the park to run off the geese. Furuto said two flashing beacons installed in the lake’s waters, at $400 each, have proved to be more effective over the past year. The algae removal will present a new test for them.

This story was originally published March 29, 2017 at 9:00 AM with the headline "Nine years after accidental fish kill, Wapato Lake to get algae treatment again."