For Immediate Release: August 14, 2026

A harmful algal bloom (HAB) has been detected in the Yellowstone Holiday area of Hebgen Reservoir, and that area is closed for water-based activities because toxin levels are high. Routine monitoring of Hebgen shows the water contains anatoxin-a, a toxin made by certain algae that can make people, pets, and livestock very sick. The latest sample results measured twice the closure threshold, so the shoreline is being closed. New samples will be taken on Monday, and the closure will be reevaluated once those results are available. 

Read the full press release here.

Closure signs will be posted at public access points in the Yellowstone Holiday area warning the public that toxic algae has been identified in the water in these areas, and that the area is closed to water-based activities.  

Rainbow Point shoreline also remains closed due to increasing toxin levels during regular sampling. Corey Springs and Savage Bay have blooms that are being monitored for toxins, but levels remain low. Caution is still encouraged wherever toxic algae is present.