A massive fish die-off at Stampede Reservoir, 19 miles northeast of Truckee, is thought to be due to an algae bloom.
“The bloom appears to be causing oxygen to lower in the deeper water, and there are hundreds and hundreds of dead kokanee and lake trout,” said fisheries biologist Amber Rossi.
The lake, which is in the Sierra County portion of the Tahoe National Forest, is a popular fishing spot.
Concerned anglers have called both the state Department of Fish and Wildlife and the Forest Service’s Truckee Ranger District office for several weeks, said Rossi, who is Fish and Wildlife’s fisheries biologist for Sierra and Plumas counties.
“We’re still getting reports,” she said Friday , “so apparently it’s still going on.”
After the first call was received Sept. 8, a Fish and Wildlife warden checked for pollution and found none, Rossi said, so she took water samples Sept. 11.
“The oxygen was lower in the deeper water,” she said. “Fifty feet down, it was 2.6 parts per million – half of what fish need to survive – and 3.6 on the surface.”
Hardest hit were the kokanee, then the lake trout – both deep-water dwellers.
“We found hundreds and hundreds of them near the dam side of the lake,” Rossi said.
The bloom does not seem to have affected the rainbow and brown trout, which live in a different part of the lake where incoming tributaries help aerate the water, she said. Nor are the large-mouth bass affected – they can survive with less oxygen.
Although “we’ve had a really low water year,” she said, there have been no reports of fish die-offs at other area lakes.
“I can’t say with complete certainty what’s happening at Stampede,” Rossi said.
Because the problem does not appear to be caused by the lake “turning over” – temperature shifts that often happen in fall and spring – or by pollution, it’s more than likely caused by the algae bloom lowering the oxygen in the deeper water, she said.
“I would think the (predicted) rain and colder weather coming in would help,” Rossi said.
In the meantime, vultures, bears and eagles are having a heyday.