Despite Fish Kill, Wapato Lake Looks Better
By Ian Demsky, The News Tribune, Tacoma, Wash.
Jul. 28–Wriggling tadpoles and baby catfish. Basking turtles. Crawling dragonfly nymphs. To scientist Rob Plotnikoff, these tiny, vulnerable forms of life are signs that Wapato Lake is on its way to recovery two days after being treated with chemicals to fight toxic algae blooms.
On Saturday, visitors to the South Tacoma park were left agog as hundreds of dead fish washed up on the troubled lake’s shores.
“I’m all for cleaning up the lake, but at what cost?” wondered resident Ryan Hess after seeing the damage Saturday.
“I don’t think you want to plan for a die-off,” said Plotnikoff, a senior scientist with Tetra Tech, a Seattle-based company hired to sample and monitor the water. “Some fish were already distressed by critically low oxygen levels. It’s the lesser of two evils. You’ve got to treat for the human health threats.”
The 34-acre lake is managed by Metro Parks Tacoma. Earlier this month, the agency agreed to pay another company, TeeMark Corp. of Aitkin, Minn., $98,000 for the water treatment to kill the algae. The treatment posed no threat to people or wildlife, the company told The News Tribune three weeks ago.
Larry Dahl, a member of the Metro Parks Board of Park Commissioners, toured the lake Sunday.
“This is not the promised outcome,” Dahl said of the algae treatment. “We’re as unhappy as the public is about this.”
Commissioners probably will get a report at their meeting tonight, he said.
From a scientific standpoint, the treatment of the lake Friday with an aluminum compound was a complete success, Plotnikoff said Sunday afternoon. The usually scummy waters had cleared, showing that the compound had bonded with the phosphorus feeding the algae and settled to the bottom.
The carpet of white alum gave the lake a blue-green cast as the sunlight reflected off its now-pale bottom.
The compound “keeps the phosphorus bound on the bottom,” Plotnikoff said. “It’s the first step in treating an urban lake that’s been ill.”
The algae made Wapato Lake among the most toxic in the state, creating a health hazard for people and pets, said Metro Parks spokeswoman Nancy Johnson. Even though the water looks and smells better, residents should stay away from it until the health officials remove posted warning signs, which might take up to two weeks, she said.
Swimmers disturbing the bottom might also mix the phosphorous back into the water, Plotnikoff said.
The main culprit for the lake’s woes is people, he said. Fertilizer in stormwater runoff carries excess nutrients into the lake, which, for the poisonous algae, is like home-delivered pizza.
Although the effects will diminish as more runoff enters the lake, the treatment should give parks planners a couple of years to figure out what to do next, Johnson said.
Staff writer David Wickert contributed to this report.
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