Harmful algae bloom temporarily closes lower St. Croix River beaches

Natural organisms stimulated by extra nutrients create unsafe water conditions.




3 minute read

A type of algae that can create toxic chemicals in the water was observed on the St. Croix River below Hudson last week, with authorities warning people to stay out of it. In high enough numbers, the organisms can produce chemicals that are dangerous to people and animals.

St. Croix County reported the bloom at Troy Beach last Friday, July 8. Green water was observed at the popular swimming site a few miles south of Hudson.

“St. Croix County Parks and Public Health have reported blue-green algae blooms in the St. Croix River near Troy Beach in the Town of Troy,” said Adam Kastonek, county public information officer. “They recommend avoiding swimming in this area until water conditions improve. Both the Parks and Public Health Departments continue to monitor the water quality in this area.”

A day before, St. Croix 360 reader David Lundeen said the algae bloom at the mouth of the Kinnickinnic River was “unlike anything I’ve ever seen in the last 10 years of fishing there.” Earlier in the week, YMCA Camp St. Croix cancelled beach activities because of the algae.

By Tuesday, July 12, there was no visible sign of the algae at several spots along the Wisconsin side of the lower river.

Bad water blooms

When large quantities of the aquatic vegetation is present, called a “bloom,” it can be dangerous for people and animals to touch or drink the water. Effects can range from skin rashes to damage to the kidneys and brain. Almost every year, pet dogs in Minnesota and Wisconsin die after swimming in water contaminated by cyanobacteria. Pet owners on the lower St. Croix should be careful about allowing their dogs in the river.

Additionally, the chemicals produced by the algae can remain in the water even after the bloom has visibly dissipated. The Wisconsin Department of Public Health says “when in doubt, stay out.”

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Blue-green algae, or cyanobacteria, are naturally-occurring organisms that can quickly explode in population under the right conditions — particularly when there are extra nutrients in the water from runoff from farm fields and developed areas, or when precipitation, wind, and other natural forces are disrupted by climate change.

According to reports prepared Minnesota and Wisconsin, excess nutrients like phosphorus are worsening the algae problem. Urban and agricultural areas are estimated to produce the same amount of nutrient runoff per acre, though agriculture takes up 795,000 acres in the St. Croix’s watershed, while urban landscapes comprise about 35,000 acres.

Too much to eat

Lake St. Croix has approximately three time as much phosphorus in it as it did before European settlement. A 10-year-old effort involving the states of Minnesota and Wisconsin, the Environmental Protection Agency, local governments, and other groups seeks to reduce it to 360 metric tons per year (one inspiration for St. Croix 360’s name).

Additionally, climate change forecasts for the region hint that it could worsen the algae problem. Global warming will cause more wet springs and dry summers, setting up perfect conditions to wash nutrients off the landscape early in the year, and then low water levels, slow flows, and warm temperatures later in the season let the algae thrive.

Counties, watershed districts, nonprofits, and other organizations have done extensive projects to reduce runoff to the river, from rain gardens and storm basins in developed areas to repairing gullies and planting different crops and using conservation practices in farm fields.

Meanwhile, a large hog production facility proposed near the upper St. Croix River could contribute even more nutrients and sediment to the river. The first full proposal for such a facility would produce more than 7 million gallons of nutrient-rich liquid manure to spread on surrounding farm fields each year. If the Cumberland LLC proposal is approved, local residents believe more related facilities will follow, turning the area into a major hog production zone.

Ancient organisms

Cyanobacteria are actually one of the oldest forms of life on Earth, responsible for producing a great deal of oxygen. Learn more with this video produced by the St. Croix Watershed Research Station, St. Croix 360, and MinuteEarth:


2 responses to “Harmful algae bloom temporarily closes lower St. Croix River beaches”

  1. Loralee DiLorenzo Avatar
    Loralee DiLorenzo

    I didn’t know this prompt for the name St Croix 360 until now – I like it!

  2. Mark Hove Avatar
    Mark Hove

    Yeah, interesting info, thanks!


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Harmful algae bloom temporarily closes lower St. Croix River beaches