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Harmful Algae in Minnesota Lakes: When in Doubt, Stay Out!

Harmful Algae

Blue-green algae, or cyanobacteria, have been around for eons. Thanks to them, we have an oxygen-rich atmosphere and the diversity of plants and animals living today. But something sinister happens when these algae are exposed to too much of a good thing, for instance, the nutrient phosphorus along with other factors algae need to grow: light, water, carbon dioxide, and nitrogen.

A secret trigger causes the tiny plants to produce a chemical that's toxic to the nervous system and liver, and irritating to the skin. The plants reproduce rapidly and can accumulate in a lake until you have a full-fledged harmful algal bloom.

Harmful Algal Blooms (HABs) seem to be an increasing problem during Minnesota's fleeting summers. Several dogs have died only hours after drinking or swimming in bloom-infested water and the toxic tiny plants are suspects in a few incidents of harm to humans in the state.

To help lakeshore owners know when it's safe to go into the water, Minnesota Sea Grant teamed up with the Minnesota Pollution Control Agency (MPCA) and the NOAA Center of Excellence for Great Lakes and Human Health (CEGLHH) to host three workshops this past spring.

The workshops were held in HAB-prone areas: Sauk Centre, Mankato, and St. Paul. They were the first of their kind in the Great Lakes to train a variety of audiences (natural resource and health managers, lake associations, local government officials) on algal ecology, identification, monitoring techniques, health risks, and communication.

Workshop presenter Howard Markus with the MPCA stressed that predicting toxic conditions is complex. "We can't predict when the toxins will be in the algae only when there's a higher likelihood."

Matt Lindon with the MPCA said that HAB algae are not always blue-green in color. "There can be reds, blues, and greys that's because they produce different pigments at different times, so color is not the best indicator of a blue-green algae bloom."

Characteristics of HABs include algae that form cakes, skins, or scums on the water's surface. Wind can pile the algae up along shore or in still waters and it can accumulate in other plant communities. "Some plants, like duckweed, are often confused with blue-green algae because the algae can accumulate with them," Lindon said.

A powerful smell frequently accompanies large-scale blooms. As the algae decompose, they can emit high levels of hydrogen sulfide gas that can cause temporary air quality problems.

"When in doubt, stay out. That's our take-home message here," Lindon said.

Steve Heiskary with the MPCA mentioned that accounts of toxic algae go back in Minnesota to the 1800s. The current increase in incidents caused him to form a work group with the Minnesota Veterinarians Association to aid in the treatment and report of sick pets. He said that the highest risk for toxic algae is associated with reduced light penetration in the water column (visibility of less than half a meter) and a high pH (greater than 9).

"If you walk into the lake up to your knees and you can't see your feet for the green scum, stay out," Heiskary advised.

Mike Murphy with the University of Minnesota School of Veterinary Medicine described several cases of dog poisoning, and one cat poisoning. The cat had been fed blue-green algae tablets by its owner as a health enhancement, but the tablets had the toxin in them. The cat developed liver failure, but lived after intensive treatment.

Annie Felix with the Benton County Soil and Water Conservation District, described a 2007 bloom in Little Rock Lake. She said the smell was unbearable and drifted miles away. The HAB killed fish, birds, and beavers, and led to closure of the swimming beach from late July through the rest of the summer. Barb Liukkonen with Minnesota Sea Grant said the workshops were well received by 100 attendees and 250 online viewers who gave the workshop positive evaluations.

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HABs in the Great Lakes: The Zebra Mussel Connection

Even though phosphorus rules were put in place in the 1970s, the incidence of harmful algal blooms is increasing in the lower Great Lakes due to the presence of zebra mussels. Sonia Joseph, with CEGLHH, attributes this to the feeding patterns of the mussels, which allow more light to penetrate the deeper reaches and cause more algae to grow. Zebra mussels change the nutrient content in the water, which benefits certain species like blue-green algae.

Stephanie Guildford, a researcher with UMD's Large Lakes Observatory recently gave a talk about HABs in the Great Lakes at the Environmental Protection Agency's Mid-Continent Ecology Laboratory in Duluth. She said that zebra mussels increase the amount of phosphorus in the benthos through their feces. She's not sure what evolutionary advantage the toxin gives the algae but suspects it could be a grazing deterrent or an unneeded mechanism left over from long ago.

By Marie Zhuikov
August 2008

Return to August 2008 Seiche

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