Every year from July through October, CRWA provides daily public notifications of water quality conditions in the Charles River Lower Basin, from Watertown to Boston Harbor. Through a system of color-coded flags, CRWA informs Charles River recreationalists when the river is safe for boating, or when a public health threat may be present due to bacterial contamination or cyanobacteria (blue-green algae).
E. coli bacteria
The presence of E. coli bacteria in water suggests contamination by sewage, which could mean disease-causing bacteria or viruses are present. High bacteria concentrations are typically observed after periods of heavy rainfall, when storm drains and sewer systems overflow and discharge pollutants into the river.
CRWA has developed mathematical models to estimate the probability of the Charles River exceeding the state's water quality standard for secondary contact recreation, or boating. The state boating standard for E.coli bacteria is 1,260 colony forming units per 100 milliliters of water (cfu/100 mL). Originally created by CRWA and Tufts University, the models use recent rainfall and river conditions to predict water quality violations and are updated periodically by CRWA. In addition, CRWA collects river samples weekly, which are analyzed for E.coli contamination to verify model predictions.
Cyanobacteria (Blue-Green Algae)
CRWA estimates health risks due to blooms of cyanobacteria (blue-green algae) based on weekly monitoring and communication with public health officials. Some types of cyanobacteria can produce toxins that can cause skin irritations and other health problems. Cyanobacteria concentrations in the Charles River Lower Basin are far less variable than E. coli concentrations.