Summer on the Snake River just got a lot less inviting. The Oregon Health Authority (OHA) on Monday issued recreational-use health advisories for Brownlee Reservoir and Hells Canyon Reservoir after water tests found elevated levels of microcystin, a toxin produced by cyanobacteria. The alerts cover stretches of the Snake River along the Oregon–Idaho border and warn that swallowing or inhaling contaminated water is the primary exposure risk. Officials are underscoring that children and pets are especially vulnerable and should be kept away from scummy or paint‑green water.
According to the Oregon Health Authority, both Brownlee and Hells Canyon showed microcystin levels greater than 10 µg/L on Monday, which exceeds the state’s recreational guideline for human exposure. The advisory list highlights areas where visible scum, mats or pea‑green accumulations are present and links to an interactive map showing affected access points. State and local agencies are continuing sampling and will update advisory status as new results come in.
What officials are advising
As noted by the Idaho Department of Health and Welfare, people should steer clear of swimming, wading or any direct contact with water in bloom‑affected areas, and take extra care to keep children from drinking reservoir water or getting it on their skin. The agency warns that boiling or filtering water collected from an affected area will not remove cyanotoxins and can actually increase the risk of illness. Pet owners are urged to keep dogs on leashes, away from shoreline scum and mats, and to seek veterinary care right away if animals show signs of sickness.
How high is too high
OHA’s advisory guidance sets the recreational use value (RUV) for microcystin at 8 µg/L, a level chosen to protect the most vulnerable recreators such as children. The agency issues advisories when measured concentrations exceed that number. The guidance document also explains how RUVs were derived and why toxin levels above the limit trigger warnings to avoid high‑exposure activities. Both reservoirs’ reported measurements put them above that protective threshold.
Recreation, pets and fishing
Officials say boating is generally allowed as long as speeds are kept low enough to avoid creating excessive spray. High‑spray activities like water skiing at speed increase the chance of inhaling contaminated droplets. The EPA and state agencies describe microcystin exposure in people as capable of causing stomach cramps, vomiting and, in some cases, liver effects. Pets can become very ill very quickly after drinking or licking contaminated water.
Fish taken from bloom‑affected areas may concentrate toxins in fatty tissue and internal organs. Agencies recommend thoroughly cleaning catch from affected spots, including removing skin and internal organs before cooking, or skipping consumption from those areas altogether.
This isn't the first time
Harmful algal blooms have appeared before in the Hells Canyon complex and the Brownlee area, and the Oregon Department of Environmental Quality has documented past HAB events and toxin detections around the Hells Canyon reservoirs. Warmer temperatures and nutrient conditions in summer months leave these Snake River reservoirs prone to recurring blooms, which is why agencies maintain seasonal monitoring programs.
Where to check and who to call
For the latest advisory status and maps, officials urge people to check state agency updates. OHA maintains the statewide cyanoHAB advisory page, and Idaho’s Department of Health and Welfare posts local notices for its side of the border. OHA has also shared the current advisory on its Facebook page.
If you or a pet may have been exposed and are feeling ill, contact your health provider or the poison center for guidance. Idaho’s release lists the poison center and local contacts for reporting suspected illnesses.
