LOVELAND — Walkers may notice a foul smell wafting in the air along the Loveland Recreation Trail south of the West First Street bridge.
When crews emptied a reservoir in December, it killed fish along a short stretch of the Big Thompson River from the bridge to a dam near South Railroad Avenue.
Hundreds of fish, mostly carp and bass, died when owners of the Ryan’s Gulch Reservoir drained the lake for repairs. The reservoir connects to the river through Ryan’s Gulch, an irrigation ditch in southwest Loveland.
Greg Gerlich, a senior aquatic biologist with the Colorado Division of Wildlife, said the fish probably died from a lack of oxygen combined with elevated alkaline levels.
“A lot of times what happens when a reservoir drains is the fish wait until the last possible minute to get out,” Gerlich said.
With low water levels, fish are unable to move downstream and are trapped in overloaded pools that lack oxygen, said Fred Renner, the Big Thompson River commissioner.
While some of the decomposing fish have been dead for 3 months, he said, some may have died recently.
Bill Beierwaltes, president of Ryan’s Gulch Reservoir, said the company released about 300 acre-feet of water so it could replace an 80-year-old head gate, which was leaking.
When full, the 80-acre reservoir is stocked with fish by the surrounding homeowners, who hold the surface and fishing rights. Less than half of the water is still used for irrigation.
Beierwaltes said the reservoir company tried several times to save the fish. First they stopped the leak with two plugs, both of which ripped loose, and then they attempted to catch the fish before they left the reservoir.
But as the reservoir shrunk, he said the water was too cloudy and moving too fast for workers to find and grab the fish.
“We were trying to be good stewards,” he said. “We spent time and money trying to do what we’re supposed to do, but we weren’t able to save the fish this time.”
With the reservoir repaired, Beierwaltes said, the homeowners association plans to stock it again.
According to division records, Gerlich said, the fish kill wasn’t extensive or damaging enough to warrant a cleanup.
He said if the river was contaminated, the state health department would take action.
“Unless it’s just overwhelmed, very often we won’t try to go pick it all up,” Gerlich said. “We let nature take its course.”