Silver Lake Drawdown: What Happened, What We Saw, and What We’re Doing About It

The Henry’s Fork Foundation (HFF) has become aware of, and is actively investigating, the recent drawdown of Silver Lake in Harriman State Park. The sudden lowering of the lake released a large amount of fine sediment downstream into Thurmon Creek and the Third Channel of the Henry’s Fork through the Ranch.

HFF was not informed before Silver Lake was drawn down. Fortunately, our science team was already in Harriman State Park and responded immediately, documenting conditions, collecting samples, and assessing the river as soon as impacts became visible.

The worst-case scenario has not happened, thank goodness. Based on our observations:

• We have not seen any dead fish, and trout appear to have moved away from the heaviest sediment. (Photos available.)
• At the Observation Deck—where turbidity ranged from 35–80 NTU—we saw trout rising and feeding in pockets of clearer water just outside the plume.
• Fish were still present in Thurmon Creek.

These are encouraging early signs. Our full team is engaged and working daily. We are:

• Collecting water samples as permission from Harriman State Park and weather conditions allow
• Running drone surveys
• Assessing fish behavior
• Tracking sediment movement through Thurmon Creek and Third Channel

We are monitoring, investigating, and advocating on behalf of the Henry’s Fork at every step. Although this does not appear to be a fish-kill event, we’re taking a thorough, science-based approach to understanding the full picture. This is an important event, and we’re working to understand how it unfolded.

To support that effort, we have:

• Filed a FOIA request for all permits and communications associated with the project
• Coordinated with IDEQ and the Army Corps of Engineers to understand the process and oversight
• Begun evaluating potential remediation options

We know this event has raised questions, and we’re committed to sharing updates as we gather more data and receive additional information from agency partners. For questions specifically about the repair project itself, IDPR is the agency overseeing the project.

If you’d like to be added to our Weekly River Update, we’d be glad to include you. You can also view our FAQ here.

The Henry’s Fork is important to all of us. We’re on it, and we’ll keep you updated every step of the way.