CRWA's Flagging Program uses a system of color-coded flags to indicate whether or not the river's water quality is safe for boating at twelve boating locations between Watertown and Boston. Blue flags indicate suitable boating conditions and red flags indicate potential health risks.
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What Do the Flags Mean? Blue flags indicate suitable boating conditions. Red flags indicate potential health risks. Consider avoiding areas where red flags are posted or make sure you wash after boating nearby.
About CRWA's Flag Color Predictions CRWA uses 3 different indicators to determine flag colors at each boathouse. (1) If any Combined Sewer Overflow (CSO) discharges took place in the past 48 hours in the Lower Basin, red flags will be flown at all boathouses. (2) If a cyanobacteria (blue-green algae) bloom is present in the vicinity, red flags will be flown at the affected boathouses for the duration of the bloom. Cyanobacteria monitoring is conducted at least every two weeks while the notification program is active and CRWA coordinates closely with the MA Department of Public Health who recommends blood advisories. (3) If CRWA's water quality models predict E. coli bacteria levels that exceed the State's recreational water quality standards, red flags will be flown at the affected boathouses. CRWA estimates E. coli bacteria levels using models that take into account a variety of environmental factors including rainfall and river flow. CRWA collects water samples weekly to verify the model forecasts.
Today's flag colors are a conservative estimate of water quality conditions. Actual water quality may vary from predictions.