Colorado Parks and Wildlife (CPW) is currently addressing a fish kill that left around 200 fish dead on the shores of Grizzly Reservoir. Alerts were raised about this environmental incident on August 18, prompting an immediate investigation. In conjunction with Pitkin County Public Health, Pitkin County Healthy Rivers, the U.S. Forest Service, and the Twin Lakes Reservoir and Canal Company, CPW has zeroed in on a few factors that likely led to the fish die-off. These include subpar water quality in the reservoir, brought on by several issues impacting the ecosystem.
Investigations carried out by CPW staff involved checking the water's temperature and pH levels, which illustrated the concerning state of Grizzly Reservoir. Rising water temperatures due to recent warm weather and low water flow contributed to the increased toxicity of metals such as copper. Despite water temperatures remaining within an acceptable range for rainbow trout, "the combination of rising temperatures and increased copper toxicity likely contributed to the fish mortality observed during this event," according to Colorado Parks and Wildlife.
Another contributing factor was the decline in water quality from Lincoln Creek, which feeds into Grizzly Reservoir. The Lincoln Creek Workgroup has been closely monitoring the creek over the years and recently noted a troubling decrease in pH levels, historically linked to higher metal concentrations in the water, particularly copper. In response to the fish kill, Pitkin County and Roaring Fork Conservancy collected more water samples on August 19, though results are still pending.
A crucial clean water source for the reservoir was also compromised. By August 10, the flows in Lost Man Creek and the Roaring Fork River had fallen naturally to such a level that no more diversions were made to Grizzly Reservoir. This resulted in less fresh water entering the reservoir, thus reducing the dilution of the already poor-quality water from Lincoln Creek, further exacerbating conditions.
As part of the reservoir's management strategy, CPW has released catchable rainbow trout into Grizzly Reservoir in July and August, ensuring the water quality is ideal for the fish. "Before stocking fish, hatchery staff take water temperature readings and test for pH levels to ensure they fall within acceptable ranges for the trout," according to reports from Colorado Parks and Wildlife. These actions are in line with CPW's role in managing state parks, wildlife areas, and outdoor recreation activities, a responsibility that significantly contributes to Colorado's economy.
