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Friday, Jun 5, 2026

Has the water in Denver’s Sloan’s Lake killed fish?

Cassis Tingley, The Colorado Sun
yes

Sloan’s Lake has experienced numerous algae blooms over the past several decades, some resulting in water so toxic, it killed thousands of fish.

The lake’s most recent die-off occurred in 2024 when at least 2,000 fish died from a toxic blue-green algae bloom. Blue-green algae blooms occur when water temperatures rise above normal levels, causing algae to over-produce. Algae can harm fish by releasing dangerous toxins or by “sucking” oxygen out of the water during decomposition, suffocating fish.

Due to its shallow average depth of 3.5 feet, Sloan’s Lake is particularly susceptible to rising water temperatures and resulting toxic blooms. As temperatures continue to rise due to climate change, scientists predict freshwater algae blooms could become more common.

Colorado Parks and Wildlife has stocked the lake with fish for recreational fishing for several decades, most recently depositing 9,500 rainbow trout after the 2024 die-off.

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