A fish kill event took place in the Eagle River last week, just downstream from Wolcott. The size and scope of the kill is still being determined, but it was believed to be caused by an increase of sediment loads due to intense rain on Tuesday, Aug. 16.

Residents along the Eagle River just west of Eagle noticed a dramatic rise in turbidity — or cloudiness of the water — as well as fish struggling and “gulping” near the surface and edges of the river. Later, numerous dead fish in and along the river were observed. Residents reported these sightings to Colorado Parks & Wildlife as well as Eagle River Watershed Council.

Mudslides and erosion on banks of a number of tributaries to the Eagle River, including Milk Creek, Rube Creek and Alkali Creek, are likely to blame for this increase in turbidity and subsequent fish kill. These tributaries drain from the Castle Peak area, north of Eagle, where the geology allows for rainwater to erode the softer rocks and soils.

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This erosion increases the amount of sediment in runoff and increases the turbidity of the water, resulting in the appearance of “milky” water that was observed in these waterways and the Eagle River this week.

These events are not unusual in Colorado or the Eagle River Valley. Sediment is natural in river systems, but when there’s as much as was observed in the waterway recently and all at one time, the gills of fish may become clogged, causing stress and even mortality.

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While it is unclear how many fish were impacted in the recent event on the Eagle River and how long of a reach was affected, the good news is that fisheries are able to recover from this natural event over time.

In 2012, the Colorado River saw a massive fish kill caused by sediment where it’s estimated that thousands of fish were killed. In 2020, Grizzly Creek and No Name Creek both saw flashing, or irritations in the fish, after their drainages burned in the Grizzly Creek fire. Both have seen spawning since these events, and the latter’s fishery nearing a full recovery.

There are ongoing conversations occurring on how to prevent this type of event in the future, but the feasibility of such a project is questionable based on the terrain of these drainages.

If you observed this fish kill event and can help determine the length of the reach, please call the Eagle River Watershed Council at 970-827-5406. If calling outside business hours, please leave a message.