Water Quality

Is it safe to swim? Is it safe to boat on the Mystic? Assessing water quality conditions is the foundation of our work – we strive to answer these questions and more. We accomplish this work through several comprehensive and long-term water quality monitoring programs.

Baseline Monitoring

Since July 2000, MyRWA has been monitoring trends in water quality with the help of a dedicated corps of volunteers. Water samples are collected from fifteen sites across the watershed and are analyzed for:

  • Bacteria: Enterococcus or E. coli

  • Total suspended solids

  • Nutrients: nitrate-nitrite, total phosphorus

  • Conductivity

  • Dissolved oxygen

  • Water temperature

  • Water color and odor

Explore Water Quality Results

MyRWA, together with the US Environmental Protection Agency (EPA), issues a yearly water quality report card for the Mystic River watershed. Baseline data is used as the basis for this annual water quality report card. Water quality grades are given to sections of the rivers and streams based on how often they comply with state swimming and boating standards.

Mystic Daily Boating Advisory

How safe is it to boat today?

Estimates of water quality conditions are generated by an automated bacteria prediction model and by additional cyanobacteria testing during the boating season. The predictions are made each day at 5 AM and are valid for the remainder of the day. For more on what the estimates mean and how they are arrived at, see the questions below. Click on the icons on the map for recent past predictions.

Mystic River

Mystic Valley Parkway (Rt 16)


Malden River

Revere Beach Parkway (Rt 16)


Upper Mystic Lake

Shannon Beach


What do the categories mean?


Boating is probably safe! The chances that E. coli bacteria levels exceed state recreational standards are low, and there is no evidence of a cyanobacteria bloom.


The chances that E. coli bacteria levels exceed state recreational standards are high, or there is evidence of a cyanobacteria bloom with concentrations exceeding state safety guidelines.


There is no evidence of elevated bacteria levels, but screening values indicate a possible cyanobacteria bloom.

Not Available

Current predictions are not currently available due to missing data or other system error.


Cyanobacteria bloom, Blessing of the Bay, Somerville, 2016. Photo by Wilder Huckleberry

Cyanobacteria bloom, Blessing of the Bay, Somerville, 2016. Photo by Wilder Huckleberry

Since 2007, the Cyanobacteria Monitoring Program has monitored cyanobacteria levels throughout the Mystic River Watershed and alerted authorities of the potentially harmful bacteria. Trained MyRWA interns take water samples in recreational areas where there is a higher chance of contact with cyanobacteria.

What is Cyanobacteria?

Cyanobacteria, also referred to as blue-green algae, are photosynthetic bacteria that grow in all types of water and are usually not visible to the naked eye except when they form colonies. Blooms often occur from the late summer to early autumn and can appear overnight. According to the Centers for Disease Control and Prevention, “some [blooms] can look like foam, scum, or mats on the surface of freshwater lakes and ponds.  The blooms can be blue, bright green, brown, or red and may look like paint floating on the water.”  

What is the risk?

Cyanobacteria blooms can starve marine plant and animal life of oxygen, sicken humans and animals, and in some cases can result in damage of the nervous system and liver. To decrease the chance of exposure to harmful blooms, avoid recreational activities such as swimming and boating in areas where the water looks discolored or there is surface scum and, of course, areas where notice of high cyanobacteria levels are posted. If you think you might have come in contact with cyanobacteria, rinse off with fresh water as soon as possible. It is important to note that pets can also be affected by cyanobacteria and the same precautions should be taken.

For more in-depth information about what Cyanobacteria is, how to spot it, and the potential health risks, visit the Centers for Disease Control and Prevention or the Massachusetts Department of Public Health webpage.

Track Cyanobacteria

You can now track cyanobacteria blooms using a smartphone! Check out the BloomWatch App