By Randy Scholfield How did this happen, and how can it be prevented from happening again?

Trout Unlimited today called for answers and accountability in the wake of a construction spill last month that killed more than 5,600 wild trout on the Big Thompson River near Estes Park.

The massive fish kill, first reported Tuesday by High Country News, happened March 7, but Colorado Parks and Wildlife (CPW) delayed reporting the accident until this week, it said, to conduct analysis of the fish kill. In a release, CPW said that “site conditions, weather, soil, topography” and other factors led to seepage from concrete work, which raised the pH of the water, killing and sickening fish in the North Fork of the Big Thompson and on the mainstem.

More than half of the trout in the 8-mile river stretch from Drake to west Loveland were killed by the spill, according to the CPW analysis.

“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.”

Nickum said TU has a number of questions about the spill.

“What mistakes or human failures caused the accident? What best practices were in place during construction to prevent a major spill like this into prime trout habitat? And what procedures or guidelines need to be changed to ensure that this kind of catastrophe doesn’t happen again?”

He added, “There need to be answers and accountability.” Nickum called for CPW to push for full financial restitution from responsible parties to offset damage to the Big Thompson trout fishery, which contributes $4.3 million annually to the local economy.

TU’s local grassroots chapters in Estes Park and Fort Collins have been involved with willow planting and other habitat improvement projects on the Big Thompson in the wake of the September 2013 floods that devastated the river corridor.

“We’re deeply disappointed that recovery work we’ve done since the flooding has taken a big hit,” said Wil Huett, president of TU’s Rocky Mountain Flycasters chapter in Fort Collins. “We’ll get back to work to rebuild habitat and fish populations in the river, but this is a major setback.”

Randy Scholfield is the TU Director of Communications for the Southwest region.