Huge fish kill in Big Thompson unreported for a month

A huge fish kill of 5,600 trout, suckers and dace in the Big Thompson occurred on March 7, 2016 below Drake to Loveland. We learned of it on April 26 in the High Country News, in the Loveland Reporter-Herald and a press release issued by Colorado Parks & Wildlife. According to its press release, “CPW delayed news on the fish kill until the data had been thoroughly analyzed.” From what we have learned, apparently the fish kill was attributable to concrete work to rebuild the road and bridges resulting from the Sptember 2013 flood. We certainly hope there are consequences for this alarming mishap – such as fines or mitigation commensurate with the magnitude of the fish kill. The next major question is how to replenish fish in the river as this river escaped whirling disease a few years ago through natural reproduction.

Below is the press release issued by Colorado Parks & Wildlife:


Jennifer Churchill

Fishkill on Big Thompson being mitigated through partner meetings

DENVER — Colorado Parks and Wildlife (CPW) confirmed today that there was a significant fish kill March 7 on the Lower North Fork Big Thompson and main stem Big Thompson River from Drake downstream to the canyon mouth in west Loveland.

The initial citizen reports prompted a multiple-agency response followed by a precautionary shutdown of water intake from the Big Thompson River by the city of Loveland. On finding that the event was limited to loss of fish including rainbow and brown trout, suckers and dace, CPW turned the focus of their investigation to verifying the origin, number of stream miles impacted, and the extent of kill.

Historic data and sample sites used by CPW for long-term monitoring of this famous recreational fishery was instrumental in defining loss to the natural resource. Before the September 2013 flood the Big Thompson fishery provided approximately $4.3 million annually on local economic impact. Restoring the recreational fishery and creating a new road-river interface with long-term resiliency and natural function remains a priority for multiple agencies, despite the latest setback.

While details of the fish kill are still being analyzed, it appears the event was associated with concrete work being performed in building and securing rockery walls
along Larimer County Road 43 and replacement of the nearby Storm Mountain Road Bridge which spans the lower North Fork, as part of the massive redesign of County Road 43 and the adjacent North Fork Big Thompson. The Storm Mountain Bridge is located approximately 0.4 miles upstream of the confluence at Drake, Colorado.

Using electro fishing, a non lethal industry standard method for estimating fish populations in rivers and streams in conjunction with citizen reports in the days immediately following the kill, CPW was able to pinpoint where fish were dying and locate the lower extent of the kill. The extent of the loss extended 8.3 miles below the confluence to Loveland’s water treatment facility where sentinel fish kept in tanks to monitor river water quality died. CPW did not find any sick or dead fish further downstream. By comparing CPW historic sites surveyed during the Fall of 2015 with post-incident surveys CPW provided a statistically accurate estimate of number of fish killed.

Ben Swigle, CPW’s aquatic biologist for the Big Thompson drainage, concluded sections of the Big Thompson River between Drake and Estes Park were not impacted and œthat healthy populations of both native and sportfish species in the upper sections will partially serve to repopulate sections of river compromised as part of
this unfortunate event. The 0.4 miles of the North Fork likely suffered a complete loss, whereas and the main stem Big Thompson from Drake downstream to the Loveland facility had suffered an estimated 52 percent loss. It is estimated that total loss was in excess of 5,600 fish.

CPW delayed news on the fish kill until data had been thoroughly analyzed. Throughout the investigation CPW worked with American Civil Constructors (ACC), the contractor for the County Road 43 flood recovery project being completed for the benefit of Larimer County under a contract administered by the Central Federal Lands Highway Division of the Federal Highway Administration, in delineating issues leading to this unfortunate event. The County Road 43 project represents a massive undertaking to rebuild the road in a manner that will be resilient to future flood
events and provide safe travel for motorists, while simultaneously restoring several miles of the North Fork Big Thompson to provide optimal flood flows and maximize aquatic and riparian habitat.

To date the project, which is slated for completion in late summer 2016, has replaced multiple bridges and constructed grouted rockery walls along many sections of road and river without issue. Unfortunately, site conditions, weather, soils, topography and other factors at the Storm Mountain Bridge created conditions that allowed movement of chemicals from concrete to enter the stream, causing a dramatic increase in pH (acidic balance of water) which when moving downstream sickened orkilled fish in its path.

Since the event, agencies involved in the Big Thompson project have been working together to establish a set of best management practices to minimize a similar event from occurring again. CPW is also working with agencies involved to determine a method of recovering the loss to the State’s fishery.

œWe have been pleased at the sincere and open effort by ACC, Larimer County, and Central Federal Lands, in working together to figure out what the problem was,
solutions to implement and now how we can work together to recover the loss in a manner that will provide long term improvement to the Big Thompson fishery, stated
Area Wildlife Manager Larry Rogstad. œWith the effort, planning and implementation that has occurred on the County Road 43 Project the public can be assured that the final result will be a safer road, improved canyon access, and a much improved river ecosystem.

Rogstad went on to say that, œWhile this has been a sad event, we hope that people will remain focused on the ultimate goal, long term and long lasting canyon recovery.

For more information on fishery management in Colorado, visit: **