Basic Information about the Charles River Buoy

Water Monitoring buoy in the Charles River outside Boston's Museum of Science.

Every 15 minutes, this self-contained solar powered buoy takes measurements. The data is transmitted in near real-time using telemetry for remote access on EPA's website. EPA scientists and water quality managers use the data from this buoy to assess water quality conditions and to help track cyanobacteria (blue-green algae) blooms.

EPA measures real-time water quality using a sonde with sensors mounted on an anchored floating buoy. The sensors on the buoy are located 1 meter below the water's surface and measure the following:

• temperature
• dissolved oxygen
• specific conductance (conductivity)
• pH
• turbidity
• chlorophyll
• phycocyanin

Live Water Quality Data for the Lower Charles River

Water Surface View

Algal Blooms

Nutrients, primarily phosphorus, are a chief culprit for dramatic algae blooms that can plague the River with blue-green algae during the summer months.

These "blue-green" algae blooms, are a form of bacterial known as Cyanobacteria, whose cells may release a toxin when they die. Exposure to the toxin can cause skin rashes and irritate the nose, eyes or throat, and if ingested can lead to serious liver and nervous system damage. Other harmful effects of the algae include reduced water clarity, nuisance scum, and reduced oxygen in the water which is necessary for a healthy fish habitat.

Saltwater Wedge

Saltwater intrusion into the Charles River Basin has long been an issue of concern. The original Charles River Dam built in 1908 helped solve one of Boston's major sanitary problems - the accumulation of untreated sewage on the tidal flats of the Charles River estuary during the low tide.

But, by building the dam it created a freshwater impoundment. Salt water is introduced by leaks in the dam and opening the locks for boaters. During low flow summer conditions the saltwater wedge expands up the river.

Wet Weather Events

Wet weather, or rain, causes several changes in water quality in the Charles. If it is a prolonged high intensity storm, it will trigger discharges from Combined Sewer Overflows carrying fecal matter and other pollutants. This will increase the amount of suspended (neither sinking nor floating) material in the Charles and can increase the measurement of turbidity. It will also dramatically increase bacterial concentrations (which are not measured by the buoy) in the River.

Most rain events cause the discharge of stormwater through the hundreds of stormwater outfalls in the Charles. Because stormwater flushes dirt and other surface pollutants into the River, higher turbidity readings can occur. If rain occurs during hot summer weather, it may cause a temporary increase in water temperature; this is a result of stormwater being heated as it flows over hot impervious surfaces such as streets, roofs and parking lots on its way to the River. Higher water temperatures will increase the likelihood of algal blooms, which trigger increases in chlorophyll and phycocyanin measurements from the buoy.

Water Quality View

Urban Runoff View

Storm drain pipes and Combined Sewer Overflows (CSOs) have long been a culprit for discharge of pollutants into urban waterways like the Charles River. Street storm drains can carry automotive fluids, fertilizers, pesticides, road salt and animal waste with rain water that can pollute the river. CSOs occur when the sewer system is overloaded and wastewater is carried through the stormwater pipes and discharged into the River.

The sediment in the Charles River is a good snapshot into its history. The layers of sediment with different levels of contaminants can show the past uses of the river and watershed.