Algae Bloom Kills Cattle at Cottonwood Reservoir in Eastern Oregon

Editor's Note: This article previously identified the Cottonwood Reservoir in south central Oregon as the affected body of water. This has been corrected: the affected body of water is in Harney County.

The Oregon Department of Agriculture announced over the weekend a suspected algae bloom on Cottonwood Reservoir in Harney County, along the eastern border of Idaho.

 Algae blooms are toxic, and fatal to most animals and even humans

A number of cattle have been found dead near the reservoir, and officials suspect it was from consuming algae-tainted water. According to ODA: 

"Oregon Health Authority (OHA) issued a Harmful Algal Bloom recreational advisory on August 1, 2024, for Cottonwood Reservoir in Harney County. Signs of cyanotoxin exposure in animals include vomiting for companion animals, increased salivation, fatigue, stumbling, shortness of breath, weakness, seizure like activity, liver failure and eventually death. Animals can ingest the toxin through direct exposure to the infected water, eating floating mats or dried crust along the shore."

All current advisories for Oregon harmful algae blooms can be viewed here.

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Algae blooms occur as a result of runoff from excess fertilizer and other nutrients into lakes and even rivers, coupled with warmer than normal weather temps. The combination often creates explosive toxic algae  growth. Numerous areas in the Pacific Northwest experience this, including Potholes Reservoir in Grant County, WA and even some activity along shore of the  Columbia River near Richland WA.

Health and ag officials caution swimmers, citizens and ag producers when it comes to suspicious looking water "when in doubt, stay out."