Environmental Services tests for bacteria, specifically E. coli, in the Willamette each week during peak recreation months - from the end of May through October, and year-round at three locations. Here's why:
Escherichia coli (E. coli) are bacteria that indicate fecal contamination and potential human health risks. E. coli indicate the presence of fecal matter from birds, rodents, pets, livestock, humans and other warm-blooded animals.
E. coli and other bacteria are natural inhabitants of the lower intestine of warm-blooded animals. A few strains of E. coli can cause serious illness in humans.
Researchers used studies at Great Lakes swimming beaches with known human sources of fecal contamination to establish safe levels of fecal bacteria based on an accepted risk of eight occurrences of gastrointestinal (GI) illnesses per 1,000 swimmers. These GI illnesses are most likely caused by a variety of bacteria, viruses and parasites present in fecal matter and not by E. coli alone.
Oregon Department of Environmental Quality rules say that no single surface water sample may exceed 406 E. coli colonies per 100 milliliters (colonies/100 mL) and the logarithmic mean of five water samples collected within 30 days may not exceed 126 colonies/100 mL.
Environmental Services field staff deliver water samples within six hours to the city's Water Pollution Control Laboratory for analysis. Lab technicians use the Colilert QT method (IDEXX Quanti-Tray®) to analyze samples. Results are typically available within 24 hours and posted at www.portlandoregon.gov/bes/RecreationIndex.