The Chicago Park District tests the water for Escherichia coli bacteria. Escherichia coli is not harmful itself and is naturally occurring in the environment. However, this bacteria is an indicator of the presence of other germs that could make you sick. US Environmental Protection Agency (USEPA) beach policy recommends notifying the public when E. coli bacteria levels are above the federal water quality Beach Action Value (BAV), which is 235*. This standard is used at beaches throughout the Great Lakes region. For more information please refer to the USEPA Recreational Water Quality Criteria.

The Chicago Park District in partnership with the US Geological Survey, has also developed statistical models that use weather data to predict the bacteria levels in real-time. These models provide information about water quality in real-time, compared to 18-24 hours to get results from a lab for traditional water quality testing. The models were developed with grant funding from the EPA's Great Lakes Restoration Initiative. When bacteria levels are detected (or predicted to be) above 235, CPD posts an advisory at the beach. *The unit of measurement for Escherichia coli is "Colony Forming Units (CFU) per 100 milliliters of water."

The Chicago Park District is piloting a new rapid testing method developed by the US Environmental Protection Agency (USEPA). The new method measures levels of bacterial DNA in beach water. Measuring bacteria in beach water by the standard method takes about 18 hours, but the DNA test gives results within a few hours. The Chicago Park District can use results of the rapid test to notify the public when the risk is elevated for developing gastrointestinal symptoms. DNA levels above 1,000* CCE are above the Beach Action Value (BAV) developed by the USEPA. For more information please refer to the USEPA Recreational Water Quality Criteria.

*The unit of measuring DNA is "enterococci calibrator cell equivalents (CCE) per 100 milliliters of water."

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