He added that a similar algae bloom has been recorded at nearby Homestake Lake, although it didn’t result in any animal deaths. But Delmoe Lake hasn’t had any such blooms.

The recent warm weather is likely a factor, de Golia said.

Blue-green algae when in the bloom growth phase can produce a cyanotoxin that is incredibly lethal, said Dr. Joe Hartley, a large animal veterinarian in Dillon. He studied blooms in lakes in northern Idaho while in veterinary school and said they could kill animals quickly.

“When it blooms in certain times of the year it’s very toxic,” he said. “We would take a cc of water, give it to mouse and it would kill it almost instantly.” To be lethal, the toxin has to be ingested, he said. But that’s possible for a person or animal just swimming in the water.

The Forest Service doesn’t plan to test the water because the results would likely take a while to come back, de Golia said. The suspected toxin gets killed by a hard frost, so officials are hoping to get a cold night to take care of the problem.

“Certainly we can’t chlorinate the lake,” he said. “We’re just going to keep people away from it until the cold weather sets in.”

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