Blue-green Algae Observed in Lake Superior
Published: July 25, 2012 by the Northern Region
Contact(s): Nancy J. Larson, DNR Lake Superior Water Quality team leader, 715-685-2913; Gina D. LaLiberte, DNR scientist, 608-221-5377, or Julie Van Stappen, Apostle Islands/National Park Service chief of resource management and planning, 715-779-3398, ext. 102
BAYFIELD, WI - Samples of a "green scum" reported by visitors to Lake Superior beaches from Cornucopia to Little Sand Bay on July 14-15were confirmed to contain a species of blue-green algae. By July 15 the algae bloom had broken up.
Many species of blue-green algae, including those collected from Meyer's Beach, are capable of producing toxins. Toxins are not produced all of the time and there is no easy way to tell when blue-green algae are producing them and when they are not, according to water quality experts. The samples collected at Meyer's Beach July 14-15 did not contain any toxins.
Also known as Cyanobacteria, blue-green algae are a group of photosynthetic bacteria that many people refer to as "pond scum." Blue-green algae are most often blue-green in color, but can also be blue, green, reddish-purple, or brown. Blue-green algae generally grow in lakes, ponds, and slow-moving streams when the water is warm and enriched with nutrients like phosphorus or nitrogen. When environmental conditions are just right, blue-green algae can grow very quickly in number. Many species are buoyant and will float to the surface, where they form scum layers or floating mats.
Blue-green algae blooms are extremely unusual in Lake Superior because the water is generally very low in nutrients and cold. However, the floods in June flushed nutrients and sediment from the land into the lake. Combined with the warm weather, conditions may have been just right for the algae to multiply. The species that was identified at Myers Beach has been known to "bloom" in other nutrient poor lakes under the right conditions.
People should exercise a common-sense approach to protection from exposure to blue-green algae. Do not swim in water that looks like "pea soup," green or blue paint, or that has a scum layer or puffy blobs floating on the surface. It can be difficult to tell if the water is "green" with algae when there is a lot of sediment in Lake Superior water as we see after a rain, so if water looks questionable, avoid swimming. The chance for health effects is greater if you or your children participate in water-related activities such as swimming, wading, water or jet-skiing, or wind surfing. Try to find areas where a blue-green algae bloom is not present.
The DNR recommends that people throughout the state shower and rinse pets after swimming to remove algae and other possible irritants. Also, keep pets out of the water under those conditions since they can lick algae from their fur while grooming.
Campers should be aware that water filtration and other field treatments may not be effective in treating the blue-green algae toxins. Avoid ingestion of water from areas in and near blue-green algae blooms. To minimize risk during this time, campers and boaters in the Apostle Islands should consider taking drinking water only from areas in Lake Superior where the water is clear and away from shallow areas.
Human health problems from recreational exposure to blue-green algae are most commonly manifested as rashes, gastroenteritis, and respiratory symptoms caused by irritants in the cell walls.
The algae bloom reported July 14-15 quickly dispersed and there were no reports from any of the Apostle Islands. People should report any new observations of algae blooms to the Wisconsin DNR at (715) 635-4034, (715) 685-2913, or to the Apostle Islands National Lakeshore at (715) 779-3398, ext. 102.