Officials close Cow Creek Reservoir near Chinook

Press release

Blaine County health officials reported Thursday that a test performed for cyanotoxins associated with a blue-green algae bloom at Cow Creek Reservoir has returned with high results.

As a result, state and local health officials recommend the reservoir, southwest of Chinook, be closed to all recreation and that pets and livestock be kept away from these waters. Closure signs have been posted at access points.

The first report of concerns came Sept. 1 when a woman reported her 10-month-old dog died after drinking water from the outflow of the reservoir.

Blaine County sanitarian collected eight water samples Sept. 12 from various places on the reservoir and from Cow Creek near the inlet and outlet. The samples were tested by the Environmental Protection Agency’s Region 8 lab in Denver with results returned Thursday. One sample taken along the north shore midway between the dam and the inlet indicated high levels of microcystin — at or above 50 micrograms per liter (>50 ug/L). The EPA’s human health recreational advisory level is 8 ug/L.   

Microcystin is a known liver toxin and the Montana Department of Environmental Quality, the Department of Public Health and Human Services and the Blaine County Health Department support this temporary closure.

Officials note that conditions on the reservoir can change rapidly for better or worse depending on factors such as wind, weather and water temperature. The high level in the sample collected along the north shore may not be indicative that the entire reservoir is affected. However, officials urge caution and want to keep pets, livestock, children and adults out of Cow Creek Reservoir until further notice.

According to DEQ, these types of algal blooms are native to freshwater lakes and reservoirs in Montana. They tend to grow in warmer water and where there’s an increase in nitrogen and phosphorus runoff from a variety of human activities. They become increasingly common this time of year. The algae blooms float on the surface of the water and may look like pea soup, grass clippings, or green latex paint.

If people see what they think might be a harmful algae bloom, they can report it using the Montana Department of Public Health and Human Services website at http://www.hab.mt.gov  The site also has a map of HAB reports and information on how to identify them.

People who suspect a toxic algae-related illness in a person or animal, including livestock, call Poison Control immediately at 1-800-222-1222 and/or contact Blaine County Sanitarian Ron Andersen at 406-868-4957.