Fish in peril after reservoir goes dry
Nov 02, 2020
Bend BulletinWhen the water level in Wickiup Reservoir dropped to critical levels in August, Central Oregon’s farming community was left without a stable source of water for irrigation. It also left thousands of fish without a sufficient habitat to survive.
Fish that remained in the reservoir until it was depleted were largely washed downstream, according to a study by the Oregon Department of Fish and Wildlife, which completed its annual fall fish sampling in the Upper Deschutes in late October.
The fish departed through an unscreened outlet at the Wickiup dam.
Wickiup Reservoir was built in the 1940s primarily to store water for the North Unit Irrigation District, whose patrons are located mainly around Madras. In addition to storing water for irrigators, the reservoir also became an important fishery for kokanee, brown trout and native redband trout. Its depletion year after year threatens not only fish but also Central Oregon’s farming communities.
Reservoirs and releases of water are managed conservatively in dry years and have more flexibility in wet or even normal water years, said Mike Britton, general manager for the North Unit Irrigation District. The depletion of Wickiup this year was due to multiple factors, he said, including requirements for the Oregon spotted frog and ongoing drought.
“Oregon spotted frog flow requirements have more water released during the spring, fall and winter that would have otherwise been saved or stored in Wickiup and Crane Prairie,” said Britton. “That foregone saved or stored water could be the difference between meeting minimum flows or potentially releasing more than the minimum.”
Britton said the drought compounds the issue and will require “several years of good winters” to rebound. Two-thirds of Deschutes County is currently in a state of extreme drought.
Wickiup Reservoir emptied in mid-September, leaving only the Deschutes River to flow through its historic channel.
Brett Hodgeson, a fish biologist with ODFW, said the escape of the remaining fish in the reservoir this year was similar to 2018, another year that saw Wickiup go dry. ODFW biologists monitored the fish that departed through the outlet, capturing large numbers of large brown trout and rainbow trout.
“The majority of the brown trout and all the rainbow likely came from the reservoir. Good numbers of whitefish and adult kokanee were captured as well,” said Hodgson.
Smaller fish were most likely swept downstream and out of the sampling area in August and September due to the strong flows coming out of Wickiup, said Hodgson. Flows out of Wickiup, for the purposes of irrigation, were 400 to 500 cubic feet per second at the time. Current flows are around 100 cfs as water is now being held back for winter storage.
The low flows coming out of the Deschutes in winter will make it difficult for the river to support viable populations of rainbow trout on a year-round basis, said Hodgson. His expectation is based on studies conducted following similar dry years.
“When we sampled in the spring of 2019 following the 2018 reservoir drawdown, the majority of fish captured in the fall were gone,” said Hodgson. “This was particularly true for rainbow trout.”
Hodgson said it’s unclear if the fish perished during the winter or simply moved out of the sampling area, but previous sampling conducted over seven years indicates that the fish are simply unable to survive low flows.
“The current release of 100 cubic feet per second during the non-irrigation season is certainly better than the previous 30 cfs. However, it is not sufficient to meet the needs of fish through their life history,” said Hodgson.
Hodgson added that drought conditions and water management are not sustainable for kokanee in Wickiup Reservoir. However, the draining of Wickiup could have a silver lining for native redband trout populations — their flight from the reservoir is expected to boost their numbers in the Upper Deschutes River.
“For this to occur, there must be an increase in flow during the winter months,” said Hodgson. “The sooner we reach a minimum flow of 300 cfs in the winter, the sooner we will be able to restore native fish populations and begin ecological recovery in the Upper Deschutes.”
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