Summer 2005



UW Sea Grant Research

Sign of the Times

Tracing Sources of Beach-Closing Contaminants Means Busy Summer for Researcher

By Kathleen Schmitt

As temperatures and humidity climb this summer, many Wisconsin residents will head to Lake Michigan beaches for relief. But instead of running into the water, beachgoers are increasingly running into bright red signs signaling closed beaches and unsafe swimming conditions.

Sandra McLellan is trying to find out why so many of these signs are showing up. With funding from UW Sea Grant, McLellan is searching for the source of contaminants along the Lake Michigan coast, hoping to arm management agencies with better information to clean up beaches.

“This information is really important for the decision makers,” says McLellan. “It’s very difficult to decide where to put financial resources to improve water quality if you don’t know where the pollution is coming from.”

Beach managers post closings when the amount of Escherichia coli (E. coli) in the water exceeds standards recommended by the U.S. Environmental Protection Agency. E. coli is a bacterium that causes minimal health risk to swimmers, but in high numbers it can indicate the presence of other dangerous bacteria and viruses that can sicken beachgoers.

Although elevated E. coli numbers can be a good indicator of poor water quality, they tell nothing about the source of the contamination. So researchers in McLellan’s lab at the UW-Milwaukee Great Lakes WATER Institute are trying to squeeze out as much information as they can from water samples taken along the coastline.

To find out if pollutants originate from humans, McLellan checks for resistance in E. coli to antibiotics, which people use and wild animals don’t. Tracing the origins of non-human pollutants can be more challenging. Possible sources range from gull droppings in the sand to rainwater that flows to beaches after running off lawns, farms, streets, or construction sites, picking up animal waste, fertilizer, pesticides, trash, and many other pollutants along the way. To weed through these possibilities, McLellan, a bacterial geneticist, looks for genetic markers in another species of indicator bacteria. Certain types of Bacteroides can be linked to fecal matter from specific host animals, such as cows or humans.

The investigative work doesn’t end in the laboratory. McLellan routinely heads out to the beaches to confirm her findings. For example, bacteria that appear to be primarily from humans would send her looking for evidence of sewage overflows or faulty sewer pipes, some of which are nearly 100 years old in certain areas of Milwaukee.

McLellan usually isn’t alone on these scientific beachcombing trips. Often accompanying her are beach managers, city officials, and others who know the territory.

“That’s why I think our research has been really successful to date,” McLellan says, “because we’re not doing it in a vacuum.”

McLellan says one encouraging finding from her research is that poor water quality at beaches doesn’t seem to be signaling that Lake Michigan as a whole is experiencing the same level of contamination.

“We’ve found that most of the E. coli we detect in these beach areas usually comes from a very localized source,” she says. “That’s good news because it means there are management practices that can be put in place to fix some of these problems.”









The Aquatic Sciences Center is the administrative home of the
University of Wisconsin Sea Grant Institute & University of Wisconsin Water Resources Institute.

©2011 University of Wisconsin Board of Regents