About 200 fish were found dead on August 18 at Grizzly Reservoir, a well-loved fishing and camping spot near Aspen, Colorado. The cause? Toxic metals that naturally occurred in the water. Colorado Parks and Wildlife (CPW) had been stocking this reservoir for over 50 years without any issues, but they started monitoring the water quality closely after a fish kill in 2021.
Kendall Bakich, an aquatic biologist with CPW, is leading efforts to measure the metal concentrations in the water. She notes that this metal toxicity is becoming a more frequent problem. “We’re seeing rivers across North America being impacted by heavy metals due to climate change,” she says.
Climate change leads to higher temperatures and droughts. This reduces the water needed to dilute naturally occurring metals, creating hazardous conditions for fish. In this case, copper is the main issue. It comes from heavy metal deposits near Lincoln Creek, which flows into Grizzly Reservoir and further into the Roaring Fork River. Bakich highlights that warming temperatures and lower snowpack mean these toxic metals have a greater impact.
This year, less water was available to dilute the metals, which further worsened the situation. Bakich expressed concern over the resources CPW has invested in raising these fish, especially since they’ve noticed fewer fish populations downstream in recent years. “Last year, I didn’t find any fish in Lincoln Creek at all,” she reported.
The impact isn’t limited to Grizzly Reservoir. Toxicity levels have also affected fish in the Roaring Fork River. Even if fish aren’t killed outright, ongoing low-level toxicity can hinder their growth and overall health. CPW is collaborating with local agencies and researchers to address this issue, although efforts to manage metals from the historic Ruby Mine are just one part of a larger challenge.
For now, fishing at Grizzly Reservoir will likely be limited. Even though the water was tested before stocking in July and August, conditions can shift quickly. By mid-August, the situation had deteriorated enough to cause significant fish deaths.
As we confront these evolving challenges, understanding the relationship between climate change and water quality will be essential for the health of our aquatic ecosystems. For more on related environmental issues and conservation efforts, check out resources from Trout Unlimited and Colorado Parks and Wildlife.
