How Do Flash Floods Impact the Fish?

Aquatic biologist Kyle Battige holds up dead trout pulled from the bank of the Cache la Poudre River on 7.20.21. Photo courtesy of CPW

Colorado Parks and Wildlife (CPW) officials are monitoring and documenting the impacts to the fishery on the Cache la Poudre River following the recent flash flood event.

A loss of fish has been observed and CPW will continue to monitor the situation, especially with the forecast and warnings of possible repeat events occurring this weekend and throughout the summer.

“We will hold off on fish population impact comments until we can collect standardized data,” said senior aquatic biologist Jeff Spohn.

Fish surveys are scheduled to be conducted on the river in mid-to-late October.

“We went up and looked around the entire canyon on Wednesday,” said Aquatic Biologist Kyle Battige. “There are dead fish, but to what quantity and where that loss is coming from at the various stretches on the river is not known at this time. There will be impacts and we will try to assess how serious those impacts to the fishery will be in the fall.”

[VIDEO] CPW assessing the river on Wednesday, July 21

Battige said the fish he saw on Wednesday were affected by the heavy sediment loading into the river from runoff on the Cameron Peak Fire burn zone.

“That can basically suffocate the fish because that amount of sediment and debris prevents the fish from pulling oxygen out of the water,” he said. “It is too early to say the true extent, but we saw impacts stretching from Black Hollow Creek all the way down to College Avenue in Fort Collins.”

Battige noted that while rainbow trout are mostly sustained through annual stocking efforts, the brown trout population in the Poudre River is self-sustaining. CPW also has the capacity, if it is determined to be warranted, to stock brown trout and rainbow trout in future years.

“CPW has a fairly robust historic data set on the fishery population in the river, generally averaging between 800-1,200 trout per mile, depending on location in the canyon,” Battige said.

Brown trout dominates those population numbers in the Poudre Canyon.

If people do encounter dead fish along the river, they should not handle the fish and leave them as they lay to let nature take its course.

You can learn more about the impacts wildfire has on wildlife, our fisheries and forests from this Colorado Outdoors podcast episode produced last November in the midst of the Cameron Peak Fire.

CPW advises residents to adhere to the warnings being issued in the weather forecast and to follow the advice and any closures put in place by the Larimer County Sheriff’s Office and the U.S. Forest Service.

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