2007 National Lake Survey - Wisconsin Results

Indicators of Recreational Value

The recreational value of a lake is measured in its ability to support recreational acitivites such as swimming, fishing, and boating. This study, however, focused primarily on the presence of harmful algae and bacteria that would prevent safe recreating. Thus, the bacteria enterococci and algal toxins from Microsystis were measured as the primary indicators of recreational value.

• Fecal bacteria
• Algal toxins

Fecal bacteria

Enterococci are bacteria found naturally in the guts of warm blooded creatures. These bacteria, by themselves, are not considered harmfull to humans but are often found in the presence of many of the human pathogens found in sewage. Epidemiological studies of marine and fresh water bathing beaches have established a direct relationship between the density of enterococci and the occurrence of swimming-associated gastroenteritis. An enterococci sample was taken in waist deep water from a nearshore habitat plot on each lake.

Algal toxins

Microcystis is a type of photosynthesizing blue-green algae (also referred to as cyanobacteria) that is found naturally in low concentrations in freshwater lakes. However, given the proper level of light and nutrients, it can join together into colonies, floating to the water surface to create algal mats. At even higher nutrient concentrations, Microcystis blooms are so dense that they resemble bright green paint spilled into the water.

Besides being unsightly, such blooms are potentially a threat to human health. Microcystis, like other blue-green algae species, produces a potent liver toxin, and other species produce a variety of neurotoxins affecting the nervous and respiratory systems. Although the likelihood of people being affected by a Microcystis bloom is low, exposure can cause minor skin irritation and gastrointestinal discomfort if ingested while swimming. Likewise, fish and bird mortalities have been reported on lakes with persistant blooms. The Survey sampled the middle of each lake for Microcystis to characterize the threat of such blooms.