About 10 people who swam there last weekend reported illnesses, according to a Tacoma-Pierce County Health Department news release and a spokeswoman.

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Thinking of beating this weekend’s anticipated heat wave in the cool waters of Lake Tapps? It’s probably time to look into other options.

A toxic algae bloom at the lake caused the Tacoma-Pierce County Health Department to urge people on Thursday to avoid Lake Tapps’ waters. About 10 people who swam there last weekend reported illnesses, according to a department news release and a spokeswoman.

“In terms of how long it will be a problem, we don’t know yet,” Health Department spokeswoman Edie Jeffers said. “We’re having some testing done, and the testing will basically confirm the level of algae for us.”

The symptoms reported by the sickened swimmers were consistent with those caused by ingesting microcystin, the news release said. That toxin can cause gastrointestinal problems and irritation of the skin and mucous membranes. In high-exposure cases, it is toxic to the liver and can be fatal. Pets and young children are particularly vulnerable, Jeffers said.

Jeffers said toxic algae has not previously been found at Lake Tapps. Department experts said recent changes to the lake’s levels of water inflow and outflow could be responsible, she said.

Data for Lake Tapps isn’t listed on a state Department of Ecology website that tracks toxic algae in lakes.

The current situation isn’t related “as far as we know,” Jeffers said, to the July 22 finding of bacteria at the lake that caused the department to close off swimming for a few days.

“It’s really early in the situation,” Jeffers said.