Two beaches operated by Washington County on the lower St. Croix River have been closed in recent days due to outbreaks of potentially harmful algae. Point Douglas Beach, across from Prescott, was the first to close. The bloom has since subsided there and the beach has re-opened. But now, St. Croix Bluffs Regional Park’s beach has been forced to close as the algae appears there.

“The blue green algae is no longer present at Point Douglas Park so the beach will reopen today, August 8,” the county says. “The blue green algae is now at St. Croix Bluffs, resulting in the swim beach being closed starting today, August 8, until the bloom is gone. The boat launch will remain open.”

Blue-green algae, or cyanobacteria, can produce harmful toxins that affect the skin, kidneys, and other body functions. It can also sicken or kill animals, such as pet dogs who might swim in the water. While common and naturally-occurring, cyanobacteria populations can explode under certain conditions, causing high levels of the toxins.

Some human activities can increase the frequency and intensity of blue-green algae blooms. Climate change effects on precipitation patterns, temperature, and other factors is one driver. Excessive amounts of nutrients flowing into the river from farm fields, urban areas, and wastewater treatment facilities can also feed the algae.

The lower St. Croix has been the focus of an extensive effort to reduce the amount of those nutrients entering the water since 2012. A plan developed by the states of Minnesota and Wisconsin and approved by the Environmental Protection Agency calls for cut nutrients in the water by 100 tons per year. (The goal is 360 tons per year, one reason for this publication’s name.)

Numerous farmers, citizens, nonprofits, and government agencies have worked over the past decade to reduce nutrient-laden runoff entering the river.