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HOLLADAY — Salt Lake County environmental health officials believe low water-oxygen levels might be behind a noticeable uptick in fish deaths in Big Cottonwood Creek.
Environmental health scientists with the Salt Lake County Health Department began tracking creek conditions around July 26 after reports of dead fish, according to Nicholas Rupp, the department's spokesman.
But Rupp said they found dozens of dead fish but "many healthy fish" during the investigation. They also found no indication of a contaminant or chemical spill, likely suggesting the some fish died of low oxygen tied to warmer water and lower creek levels because of summer water diversions.
"It unfortunately happens this time of year; it's not uncommon or unexpected," he wrote in an email to KSL.
Utah Division of Wildlife Resources spokeswoman Faith Heaton Jolley said many of the fish that died were white bass in the lower portion of the creek. It was enough for wildlife officials to classify it as a "fish kill."
Most of the reports came near the Creekside area of Big Cottonwood Regional Park, where the creek flows through on its way west toward the Jordan River, but he added that could be because it's a visible section of the creek where many people recreate.
It wouldn't be the first time low oxygen levels killed off a bunch of fish in a Salt Lake County body of water this year. The Utah Department of Environmental Quality last week wrapped up its investigation of about 500 fish that died at The Cove at Herriman Springs in Herriman in June, finding that the fish likely died of low oxygen levels. Agency officials said pesticides that killed off vegetation in the water plus hot conditions led to the low oxygen levels.
This summer has been hot and dry after a second-straight above-normal snowpack. Salt Lake City posted its eighth-hottest July on record after its second-hottest June since the National Weather Service began tracking data in 1874. That type of heat mixed with below-average summer rainfall is behind drying conditions across the state.
Both can also produce lower oxygen levels in bodies of water. Utah wildlife officials point out water warms as levels drop and warmer water holds less oxygen than cooler water.
"The combination of high temperatures and low oxygen can stress fish, causing poor growth and disease," Utah Division of Wildlife Resources' sportfish coordinator Randy Oplinger said in 2022, as the agency explained drought could impact fishing that year. "Fish can also die when temperatures are too warm or the oxygen levels get too low."
