Low dissolved oxygen levels in the Provo River below Deer Creek Dam haven't killed any trout, but the lack of oxygen has left many listless.
"Their physical condition is pretty good. They just don't have much energy. They're lethargic," said Charlie Thompson, Division of Wildlife Resources regional fisheries manager.Wildlife officials last week completed a five-month study of a two-mile stretch of river beginning near the dam to determine what impact low oxygen levels have on fish. "We've known we had low dissolved oxygen up here for years and we just wanted to see if we could do something about it," he said.
Water let through the dam in mid-July comes from oxygen-depleted depths of the reservoir.
Deer Creek Reservoir stratifies into layers as the summer progresses. "There is no dissolved oxygen. The DO level goes to zero," Thompson said. When that water flows downstream it chokes the plentiful brown, rainbow and cutthroat trout. "The fish just had to move out of there," he said.
Thompson and others tagged fish in April to track their movement between four 1/10-mile-long stations spread over two miles of river. They also weighed, measured and examined fish to gauge their viability. Wildlife Resources is asking fisherman who catch fish with yellow tags protruding from their backs to notify the division of the precise location.
Although oxygen levels were lower upstream near the dam, Thompson didn't find the fish population as sparse as he'd expected.
"I just didn't think there would be any left. I thought they'd all move downstream," he said. "They don't have the energy, but they're still there."
Wildlife officials didn't find any dead fish in the study area, unlike a two-mile section of the Provo River below 1300 West in Provo where about 1,500 brown trout and 500 whitefish died last month due to a severe lack of oxygen from low water flows.
Thompson said Wildlife Resources found at least two ways to put more oxygen into the water drawn from the reservoir. Raising gates just below the dam creates a waterfall that put oxygen into the river. Officials can also inject oxygen into the dam's turbines as they churn the water. Both measures are fairly compatible with the operation of the dam, he said.
Wildlife Resources might do a follow-up study in October when oxygen levels rise as the reservoir turns over, Thompson said. The division is also working with the Central Utah Water Conservancy District and the Bureau of Reclamation.