Bad Mix of Chemicals May Be to Blame for Dead Fish in Wapato Lake
By Niki Sullivan, The News Tribune, Tacoma, Wash.
Jul. 29–A faulty batch of chemicals might have caused the pH level of Wapato Lake to plummet during an algae treatment Friday, suffocating large numbers of fish, according to the company hired to monitor water quality.
Rob Plotnikoff, a senior scientist with Seattle water monitoring company Tetra Tech, told the Metro Parks board of commissioners Monday that the lake is safe now, but they’ll have to wait for more information — including a fish necropsy — to determine the exact cause of the fish kill.
The $98,000 algae treatment was supposed to be a simple way to kickstart a decades-long fight against toxic algae in the lake: An aluminum solution would be added to the water, bind with phosphates, which algae feed on, then sink to the bottom of the lake. There, it wouldn’t be available to fish, aquatic life or, most important, the algae.
By Saturday, the lake’s usual yellow-green haze had cleared, meaning the treatment had worked. But hundreds of dead fish of all sizes had floated to the top of the water, leaving scientists puzzled and community members disgusted.
By Monday’s meeting, some of those who live near the park had gotten over the initial shock: Several community members who spoke during the public comment portion of the meeting said fish could be replaced, but that the prostitutes and drug dealers that plagued the South Tacoma park were a more pressing concern.
“It’s too bad that a great plan had kind of a problem, but after all, they’re fish,” said Marcia Osborne, who lives near the park. “They can be replanted. There are other issues at Wapato Park that need to be addressed,” she said, including transients, drug deals and what she called an inattentive police force.
Before ending her three-minute comment, Osborne gestured to her service dog by her side: “I’m not against animals, as you can see,” she said, to excuse her seemingly anti-fish sentiments.
Plotnikoff told the board that pH changes were to blame for the fish kill. Initial tests showed no change in pH, which is what scientists expected, he said. By the end of the day, pH had dropped from 8 — or about the acidity of seawater — to 4.5 — more acidic than acid rain or coffee.
He said scientists have two theories about what happened: Either the chemical supplier was “caught by surprise” at the quantity of the order and had to rush through processing it, possibly meaning more acid was used, or it used a lower-grade acid than what was called for in the contract, meaning the treatment might have contained impurities.
Either way, he said, metal toxicity is not the issue: Aluminum bonds with phosphate unless pH drops to 1, which is about as acidic as stomach acid.
Commissioner Larry Dahl, who toured the park Sunday to assess the damage, said he also noted that the hose used to apply the chemical had burned a strip in the park’s grass. Plotnikoff said that was a sign the chemicals, which are mixed at 200 degrees Fahrenheit, might have been applied too hastily.
Neither Plotnikoff nor the board of commissioners addressed whether Sweetwater, the Minnesota-based company that applied the chemical, or the manufacturer was to blame for the fish kill. Representatives from the companies were not at Monday’s meeting, nor did they provide a statement.
Plotnikoff said the best course of action was to wait a few weeks while the solution continues to work in the water. During that time, he said, Tetra Tech will continue to work with the City of Tacoma, the company that applied the chemicals, and others involved to figure out what happened.
Dave Osborne, another Wapato Lake-area resident, said some good came of the treatment.
“This morning I went for a walk. It was nice to see the bottom of the lake — I seen three bicycles, a boat and a garbage can,” he said.
Niki Sullivan: 253-597-8603
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