A screen intended to prevent nonnative fish from escaping during the expansion of Elkhead Reservoir has failed.
Researchers are working hard to assess the effects, but at least some of the fish from Elkhead have turned up in the Yampa River. The fish are unwitting actors in a human drama that seeks to balance sport fisheries with the ecology of the river basin.
The failure was caused by heavy runoff.
Researchers have netted some black crappie and bluegill in the Yampa since the failure -- they are relatively benign, but they serve as indicators that other more aggressive fish may be escaping.
Some of the nonnative fish compete with endangered native fish farther downstream in the Yampa.
Pat Nelson of the Upper Colorado River Endangered Fish Recovery Prog-ram had a contingency plan in place in case of such an incident. However, for safety reasons, the screens won't be repaired until snowmelt subsides.
"There was a U.S. Fish and Wildlife Service crew working the stretch of the Yampa between Hayden and Craig," Nelson said. "We alerted them immediately, and they began concentrating on the stretch below Elkhead."
Nelson, who is the recovery program's nonnative fish management coordinator, said he learned of the screen failure May 7.
Dan Birch, project manager for the Colorado River Water Conservation District, said the original dam spillway did not have a screen at all. The temporary screen was put in place this spring to afford extra protection for the temporary spillway. The screen was 8 feet high and 80 feet long and was anchored by steel pipe set in holes bored into a concrete slab by a drill rig. However, the pressure of the water (flows in Elkhead Creek are about 1,000 cubic feet per second) separated the screen where panels of the wire mesh were joined.
Nelson said Tuesday that a few black crappie and bluegill, and a single largemouth bass, almost certainly from the reservoir, have been netted in the Yampa River downstream from the confluence with Elkhead Creek. Nonnative fish are known to compete with, and in the case of northern pike, eat endangered native fish such as the Colorado pike minnow. There is an ongoing effort to remove the nonnatives from the Yampa and Green rivers to allow populations of natives to recover.
The crappie and bluegill caught since the screens failed have been euthanized. However, Nelson said there is no conclusive evidence that the more predatory northern pikes have escaped into the Yampa. Management policies in the stretch just upstream from Elkhead confluence to Craig remain the same -- netted pike are not being killed but are being removed to other waters.
"Sam Finney's (U.S. Fish and Wildlife Service) crew seems to think pike have escaped, but we don't know that yet," Nelson said. "They found hundreds of small pike in a backwater just above the confluence, but I think they were produced there. I think that's just their spawning habitat."
The pike, crappie, bluegills and bass in Elkhead, together with four species of endangered native fish, are the focal point of a complex human partnership that has succeeded in bringing water developers and advocates of endangered species together. The capacity of the reservoir, originally opened in 1974, is being expanded from 13,700 acre-feet to about 25,700 acre-feet.
The expansion would devote 7,000 acre-feet to ensure adequate streamflows for the endangered fish during the low-water times of the year. In exchange, water developers such as the Colorado River Water Conservation Dis-trict are able to increase water storage for human needs. The water for fish at Elkhead will leverage water projects elsewhere in the basin.
Birch said his organization is monitoring incidences of escaping fish and making plans to replace the screen as soon as it's safe to do so.
"Unfortunately (the screen) failed shortly after it was installed," he said. "It's not possible to either make repair or install a new screen without putting people in the water -- a considerable safety risk. Because of the risk, we've decided to install a new screen after flows subside, probably late this month."
Angela Kantola, assistant director of the Recovery Program, said it will take time to analyze the data being collected by the USFWS crew this month and then compare it with numbers of nonnative fish in specific reaches of the Yampa from previous years.
Birch said the benefits of the Elkhead expansion project will overshadow any setback represented by the failure of the screens.
"While we regret that the screen failed, it's important to keep in mind the long view that we'll end up with a reservoir with permanent screens (at the) outlet, unlike the existing outlet. We've also designed the new spillway so that a screen can be added in the future if the Recovery Program wants."
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