By Lauren DiSpirito

LOVELAND, Colo. (CBS4) – In another setback for the Big Thompson Canyon, flood damage repair work last month caused a fish kill, decreasing a portion of the river’s wild trout population by more than half.

On March 7, chemicals from concrete work along Larimer County Road 43 near Glen Haven seeped into the water, sending a plume downstream, sharply increasing the river’s pH level, and sickening and killing more than 5,600 fish, according to Colorado Parks and Wildlife.

(credit: Colorado Parks & Wildlife)

(credit: Colorado Parks & Wildlife)

Rainbow and brown trout, suckers and dace were among the types of fish impacted. CPW estimates a 0.4 mile section of the North Fork suffered a complete loss, while an 8-mile stem of the Big Thompson from Drake to Loveland lost 52 percent of its fish.

In an interview Wednesday, Area Wildlife Manager Larry Rogstad called the fish kill “one more blow” for a region already suffering.

“Everyone’s desire since the floods has been to get this canyon restored, both the highway and the river, the homes; try to get back to a sense of normalcy,” Rogstad said. “So when you have an event like this, it takes everyone back.”

CPW first got word of the fish kill from residents who spotted dead trout along the Big Thompson’s banks, and Colorado Department of Transportation crews who were doing survey work that day. Workers reported seeing the river turn a murky color and described feeling the water have a dry quality to it, according to Rogstad.

“For whatever reason, on March 7, because of the topography, because of local soils, because of the water flow that day, temperatures, something happened,” Rogstad said.

(credit: Colorado Parks & Wildlife)

(credit: Colorado Parks & Wildlife)

The fish kill comes at a time when wild trout populations had finally started rebounding from the devastating effects of the September 2013 flood and an additional high water event in 2015. It also comes amidst ongoing efforts to restore the Big Thompson’s natural vegetation and habitat.

Colorado Trout Unlimited released a statement Wednesday calling for accountability.

“This is body blow to the Big Thompson that sets back efforts by several partners, including TU, to restore the wild trout population in the canyon,” said David Nickum, executive director of Colorado Trout Unlimited. “The Big T is a very famous and popular river with anglers, and we’re deeply concerned about how an accident of this magnitude could have happened.”

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Nickum also wants the state to push for full financial restitution.

Rogstad says CPW decided not to publicly release information about the fish kill until now, after it had completed its background investigation into what happened. During that investigation, CPW says the contractor doing the work was forthcoming.

“By no stretch of the imagination was this an act of negligence,” Rogstad said. “It was something that happened.”

Prior to 2013 flooding, the Big Thompson fishery contributed $4.3 million to the local economy each year. Since, stakeholders have been trying to come up with ways help restore the fishery to a level that’s even better than what it was before. Following the fish kill, Rogstad says the contractor involved will have a role in recovery efforts.

RELATED STORIES: September Flooding 2013 Story Archive

“We’re looking at long-term restoration to recover the loss, and recover it in a manner that will be more long term and resilient that just someone paying a fine,” Rogstad said.

CPW can pursue legal action in the incident.

Lauren DiSpirito is CBS4’s Northern Newsroom reporter. Follow her on Twitter @CBS4Lauren. Share your story ideas with her here.

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