Sediment washed through the Black Canyon Dam kills fish

The water is low in the Payette River which recently helped Idaho Fish and Game conservation officers and biologists inspect sediment deposits created from the Black Canyon Dam water draw down. The draw down is part of the scheduled construction plan of a third hydroelectric generating unit at the Black Canyon Diversion Dam. The generation plant was proposed by the U.S. Department of the Interior Bureau of Reclamation to provide power to 9,359 homes outside of Gem County.

Recently, a team of Idaho Fish and Game biologists surveyed the Payette River from the Black Canyon Dam to the Letha Bridge. The team consisted of Senior Regional Research Fisheries Biologist at IDFG Martin Koenig, IDFG Fisheries Biologist Joe Kozfkay and Emmett IDFG Conservation Officer Paul Alexander. What the group found was surprising.

During the basic fish kill and habitat survey, the IDFG biologists found more than 100 dead fish up and down the banks of the Payette River scattered below the dam to the Gem Island Sports Complex. Six different fish species were discovered dead. Koenig said that suckers, chiselmouth, pike minnows, yellow perch, carp and some small mouth bass were found floating in the river, stuck in deep sand bars or on the banks.

Kozfkay was most alarmed by the amount of deep sediment in the stream channel. It was higher than normal below the dam and also had filled pools and cracks. Sand and sediment in the water column can affect the fish’s gills, eyes and skin. “It’s like getting sand blasted,” Kozfkay said. “Many of the carp we studied were beat up.”

“When the sand fills in the small spaces, it also kills insects, crayfish and small fish which fish feed on,” Kozfkay said.

The sediment from the dam originates from upper drainages according to IDFG officers. The sand fills the pools and the fish cannot see to feed by sight. The big concern is the sediment, when washed out by high water, will be pushed into back water sloughs and channels occupied by groups of nesting and breeding duck populations.

“There is a high probability the sediment has hurt the fish population from the dam to Emmett. The fish food base was also damaged,” Kozfkay said.

Later this summer, IDFG officers will submit a mitigation request for reservoir restocking costs to re-establish fisheries. In future years, they will repeat surveys and data collection and make additional mitigation requests.

“I’m aware how important this fishery and reservoir is to the community,” Kozfkay said. “Fishing and floating the river is popular. We need to take a serious look into this and try to look for a solution.”

To contact Idaho Fish and Game call 334-3700 and the U.S. Bureau of Reclamation call 378-5020.