The county based its study on eight different sites, each selected because they were considered popular swimming holes, said Kyle Schmeck, county director of water-quality management. ``After Deep Creek Lake closed, we wanted to know where people were swimming,'' he said.
Health officials found the swimming areas by word of mouth and by spotting rope swings along the banks of the creeks and streams.
Bacteria levels have been tested at each site twice a month since the beginning of May. If test results were above the health standard of 235 colonies per 100 milliliters, the health department notified the appropriate municipality and asked that swimming be banned there.
``We wanted the townships to be aware of it. However, we don't have the authority to prevent people from swimming. We left it up to the townships to handle it,'' Schmeck said.
In the most recent tests, on Aug. 22, sections of Skippack Creek in Evansburg State Park, and the Perkiomen Creek in Upper Providence and Upper Salford Townships all had E. coli levels above 235 colonies per 100 milliliters.
Five other testing areas have all recorded higher-than-acceptable levels at one time or another during this swimming season: Perkiomen Creek in Collegeville off Route 29, the East Branch of the Perkiomen off Haldeman Road in Lower Salford, a section of Perkiomen Creek in Lower Frederick, Unami Creek in Marlborough, and Swamp Creek off Neiffer Road in Lower Frederick.
The highest level recorded was on July 24, when E. coli bacteria levels hit 1,680 colonies per 100 milliliters at the East Branch of the Perkiomen off Haldeman Road.
Schmeck said his department had long suspected geese to be the major bacteria culprits.
The county is also investigating whether malfunctioning sewage-disposal systems have contributed to the problem.
He cautioned that it may be that these creeks have always had fluctuating levels of bacteria. The health department became aware of the problem only after it started monitoring levels last year.
``We are a young department, and we don't have a lot of . . . data,'' he said.
So far this year, the county has not received any reports of residents suffering from rashes, intestinal disorders and other illnesses from swimming in the monitored waters, he said.
Reports of bacteria in the Skippack Creek in Evansburg State Park do not alarm park manager John Gribosh, who said that swimming has not been allowed at the park anyway.
``You'd be hard-pressed to find a place where you could swim,'' he said. ``It's about a foot-and-a-half deep in most places.''
Gribosh attributed the bacteria problem to geese and the weather. Bacteria thrive in slow-moving creeks in the later summer, he said.
``It's not feasible to drive all the waterfowl off,'' he said. ``There's no control of Mother Nature, but once the season changes, the bacteria counts will drop dramatically.''