Lower St. Croix included in national study of toxic algae

Scientists are working to understand when, where, and why algae can produce dangerous chemicals.




3 minute read

Microcystis algal bloom (NOAA)

The St. Croix National Scenic Riverway is one of 12 freshwater National Park units around the country that federal scientists are studying for the presence of toxic chemicals produced by certain algae. The research project began this summer and will continue until 2023.

Harmful algae blooms (HABs) are natural, though they can be stimulated by human actions, like increased nutrients in runoff from farms and cities, or warmer water attributed to climate change. Lake St. Croix is designated as impaired by authorities because of such excess nutrients. Efforts are underway to reduce runoff and lower the amount of phosphorus in the water.

The ancient organisms called cyanobacteria produce a variety of chemicals that can be harmful to humans and animals, from causing itchy skin to permanently damaging the brain, liver, kidneys, or heart. Pet dogs are particularly at risk, with a few usually dying around the region each year after going into contaminated water.

The new study will look into a key question about the risk. Blooms of harmful algae are often visible to the naked eye, appearing as thick green scum on the surface and in the water. It is often compared to green paint spilled on water. But there can also be toxins present even when algae is not visible, whether before or after it becomes obvious, or even if a bloom is never apparent.

“It’s important that we cover this wide range for both the toxins and sites in order to fully understand the extent of harmful algal blooms,” said Victoria Christensen, USGS project co-lead. “Therefore, we are also sampling a diverse range of waterbodies, such as rivers, lakes, coastal shorelines and backwater areas, that may harbor different types of blooms and different toxins.”

The team has developed new low-cost and efficient methods and tools for the monitoring effort. They will regularly measure water conditions and levels of algae and toxins. This might help park managers better predict when toxic algae may be present.

As a pilot partnership, the two agencies are trying to develop ways for the National Park Service to easily monitor for toxins and respond quickly, taking action like closing beaches.

“We are very excited about this multi-agency collaborative effort,” said Jennifer Graham, USGS project co-lead. “The end goal is to provide the information necessary for the National Park Service to develop comprehensive guidance on HAB monitoring, toxin testing and rapid response protocols.”

Microscope photo of Microcystis aeruginosa, collected from South Center Lake in the St. Croix River watershed. (Adam Heathcote/St. Croix Watershed Research Station)

Scientists from the National Park Service and U.S. Geological Survey began the research this summer. On the St. Croix, they chose St. Croix Bluffs Regional Park to closely watch over the course of three summers.

“We’re finding HABs in new areas,” said Jamie Kilgo, project co-lead and marine ecologist at the NPS. “We need to monitor areas where they are a known issue and anticipate where we might find them in the future so we can protect visitors, pets, park staff, volunteers and wildlife.”

In addition to taking frequent samples to analyze, the St. Croix Bluffs project includes two time-lapse cameras, according to Marian Shaffer, aquatic biologist at the St. Croix National Scenic Riverway. She also shared that the scientists took samples at two other sites where cyanobacteria were spotted on the river this summer, in Taylors Falls and Bayport.

Analysis is ongoing, but a particular type of harmful algae, the Microcystis family, dominated two of the samples so far.

“Microcystis communities are of concern as they produce harmful toxins which can cause serious illness in people and mortality in livestock and pets,” Shaffer says.

Learn more about the fascinating cyanobacteria, which are some of the oldest forms of life on Earth, in this video produced by the St. Croix Watershed Research Station and MinuteEarth:


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Lower St. Croix included in national study of toxic algae