Thanks to the historic cleanup of the Charles River, it is now safe to boat on the river most of the time. However, on some days the water quality in the Charles River does not meet public health standards for boating, especially after a heavy rain. On those days, although boating is still permissible, some people choose to stay off the water or take extra precautions.
Kayakers in the Charles River. Photo by Andresmh
To help the public stay informed throughout the summer, CRWA's Water Quality Notification (a.k.a. ‘Flagging’) Program alerts boaters downstream of the Watertown Dam when the Charles River is not safe for boating downstream of the Watertown Dam. Color-coded flags posted online and flying at partner boathouses notify boaters of water quality. This program encourages the public to enjoy all that the Charles River has to offer while staying safe and healthy.
What are possible health risks?
Despite the improved water quality in the Charles River, it remains crucial that boaters are aware of the potential health risks they face when coming in contact with the river. These health risks include:
1. Harmful bacteria are present in the Charles River in higher concentrations after periods of heavy rainfall due to sewer overflows that impact the river. Exposure to the bacteria and viruses commonly found in sewage can lead to infections, gastrointestinal distress, or other more serious health concerns. Health risks typically decrease within 48 hours after the storm.
2. Cyanobacteria (or blue-green algae) occur in hot, sunny, and slow-moving parts of the river. Their growth increases when excess nutrients including nitrogen and phosphorus are present, usually introduced into the river by stormwater runoff. Cyanobacteria can release toxins which are released into the water as they die and break down. Bloom advisories remain in effect for a minimum of three weeks to account for the risk of exposure to toxins when the cyanobacteria die.
How do I know if it is safe to boat?
- Before you go out on the water, check the Water Quality Notification page. This page is updated automatically several times a day using data from our weather station.
- Join our email list to receive notifications of changes in water quality.
- Follow us on twitter for daily updates.
- While on the river, check out the flags flown at one of 10 boathouses in the Lower Basin.
What do the flag colors mean?
A blue flag flown at a boathouse on the Charles River
A YELLOW flag indicates inconclusive data to preclude possible health risks. Yellow flags are often flown when a cyanobacteria bloom has been identified.
A RED flag indicates potential health risks. Red flags are flown when the models predict bacteria concentrations will likely be above 630 cfu/100 mL and for 48 hours following a CSO at Cottage Farm.
How does CRWA determine which flag to fly?
To decide which color flag to fly that day, CRWA uses actual water sampling results to build models that predict water quality from weather data. CRWA continues to verify these predictions, identify cyanobacteria blooms, and improve our models by collecting water samples at least once a week.
What are additional ways I can reduce my risk while boating?
- Wash your hands with soap and water after going out on the river and especially before eating.
- If you eat while out on the river, make sure your hands are clean and your food is protected from splashing water.
- Protect the mouthpiece of your water bottle from coming in contact with the river water.
- If you fall into the river, shower as soon as possible.
- Avoid touching your mouth or eyes while out on the river.
- Discourage your dog from drinking large quantities of river water, especially during a cyanobacteria bloom.
- Never drink the river water.