SwimCast forewarns of high bacterial levels at beaches
BY KAREN BERKOWITZ email@example.com June 18, 2013 7:26PM
Nicole Dean checks the water temperature off the north beach at North Point Marina Monday. | Joe Cyganowski~For Sun-Times Media
Percent of samples exceeding safe-to-swim standards, 2011
Rosewood Beach, Highland Park: 9%
Forest Park, Lake Forest: 7%
Sunrise Beach, Lake Bluff: 4%
Illinois Beach State Park, North Beach: 11%
Illinois Beach State Park, Resort Beach: 18%
Waukegan North, Waukegan: 4%
Waukegan South, Waukegan: 12%
North Point Marina, Winthrop Harbor: 4%
Source: Testing the Waters: Illinois, Natural Resources Defense Council
Updated: August 18, 2013 2:32AM
The sandy beaches that dot the Lake Michigan shoreline appear postcard perfect, but some frequently hide high levels of bacteria.
Regular water testing can flag problem beaches with ongoing bacterial issues, but it’s of little use in protecting swimmers against sporadic events that spike bacterial counts above safe levels.
To change that, the Lake County Health Department has been using a predictive model at selected beaches, including Rosewood Beach in Highland Park, to foretell when bacterial counts will reach unsafe levels. The other beaches where the SwimCast system currently is in use are Forest Park in Lake Forest and Waukegan South in Waukegan.
Beaches then can be closed the day bacterial counts are high, rather than the following day.
The Lake County Health Department collects water samples from beaches between Memorial Day and Labor Day and recommends a ban when E. coli counts exceed the standard of 235 colony-forming units per 100 milliliters of lake water, or about one-fifth of a pint. High E. coli counts suggest the presence of pathogens like cryptosporidia and gardia lamblia that cause waterborne illness such as gastroenteritis.
The samples, however, must be taken back to a laboratory and put through a culture that takes 18 to 24 hours. So health officials — and swimmers — typically learn after the fact that bacterial levels were high the day before. Bacterial counts may already have returned to acceptable levels on the day the beach actually is closed.
“We find out tomorrow what the water results were like today,” said Mike Adam, senior biologist with the Lake County Health Department’s environmental services division. “If I close the beach based on yesterday’s water sample, I really should have closed it yesterday.
“It is always a day late,” he added. “It is fine if the samples are bad on repeated days, but it doesn’t help on a single bad day.”
In 2011, 12 percent of water samples collected from Lake Michigan beaches in Lake County exceeded the safe-swimming standard, according to a report published annually by the Natural Resources Defense Council.
With SwimCast, however, data is collected round-the-clock on air and water temperature, wind speed and direction, precipitation, humidity, wave height, light insulation and other factors. The data is run through a computer model that helps forewarn when bacterial counts will climb above acceptable levels. The data on lake conditions also is posted and updated hourly on the health department’s web site.
Adam said the beaches selected as SwimCast sites are neither among the best or worst when it comes to high bacterial counts.
In 2011, high bacterial counts occurred in 9 percent of the samples collected at Rosewood Beach, according to the NRDC report. Meanwhile, Lake Forest’s beach showed unsafe swimming levels in 7 percent of samples, while Waukegan South’s figure was 12 percent.
“There are a number of sources of E. coli and different beaches have a different source,” said Adam.
In areas with ravines, small leaks in sanitary sewer lines can cause bacteria to flow into the lake. The county health department previously has worked with the city of Highland Park to identify and correct sanitary sewer issues.
The North Point Marina Beach in Winthrop Harbor has been among the region’s worst beaches for high levels of harmful bacteria, attributed to its high seagull population. Adam said an accumulation of sand expanded the beach’s size from roughly 1 1/2 to 10 acres, drawing more seagulls.
Yearly rates for unsafe swimming counts at North Point Marina Beach ranged from 34 to 83 percent over six years, according to the Natural Resources Defense Council’s report.
“At times, there will be 1,000 gulls at North Point Marina Beach. That is an easy thing to figure out and deal with,” said Adam.
The health department is using funds from the Great Lakes Restoration Initiative to plant native vegetation, restore the dunes and remove invasive species. The project is expected to improve water quality and reduce the number of swimming bans.