No swimming
The Muddy River in the Back Bay Fens
— Photo by Another Believer
Edited from a Boston Guardian article by Jules Roscoe
(Robert Whitcomb, New England Diary’s editor, is chairman of The Boston Guardian.)
Water quality in the Charles River and its Muddy River tributary decreased this past year, due to illicit sewage discharges, a statewide drought and a massive cyanobacterial bloom.
The Charles River Watershed Association (CRWA) released its annual water quality report card last week. The report monitors bacterial levels and instances of sewage overflows in different parts of the river. Every year, the association evaluates a three-year average of data to determine how much of the time the river was safely swimmable.
The Muddy River, which runs through the Fenway, was the most polluted part of the Charles watershed. It earned a grade of C, one step below its grade of C+ last year. Though cleanup efforts continue to be made, it has consistently been the river’s most polluted above-ground tributary. Its grade means it’s safe for swimming between 55 and 70 percent of the time.
“Ultimately, the biggest factor for the grades in the Muddy River is that it passes through a lot of urban areas,” said Marielena Lima, the CRWA who handles water quality monitoring programs. “It passes through a lot of major highways like Route 9 and I-90. All of these are opportunities for stormwater runoff pollution, unfortunately, to go into the Muddy River.”
A second factor is combined sewer overflows (CSOs), which happen because Boston’s stormwater drainage pipes are connected to its sewage system. When heavy rains overload the storm drains, the stormwater can sometimes mix with raw sewage before it drains into the river. The Muddy River didn’t have any CSOs last year, but it did experience a few in prior years, which are still counted towards its grade because of the three-year average used by the CRWA. Yet another factor is that there are some illicit sewage discharges that dump straight into the Muddy River.
“There are pipes and sewage system infrastructure that allows for discharge that shouldn't be going into the Muddy River,” Lima said. “The main thing is just detecting where those illicit connections are, so that the city can actually fix them. That’s something that the city of Brookline and the city of Boston have been working on for years, but that is still a problem.”
The lower basin of the Charles, which runs along neighborhoods like the Back Bay and Beacon Hill, earned a grade of B-, also one step below last year’s B. This means that it was safely swimmable between 70 and 85 percent of the time. The reason for this decrease was a massive cyanobacterial bloom that lasted for over 80 days, from late July nearly to the Head of the Charles Regatta in October. “Generally in the lower basin, we have more elevated phosphorus levels from stormwater runoff pollution,” Lima said. Phosphorus is a limiting nutrient for cyanobacteria and algae, which means that its concentration largely controls how much bacteria can grow. “But a big factor was the fact that we were in a drought last year.”
During a drought, the Massachusetts Water Resource Authority will conserve water in the river to prevent water levels from dipping too low by closing the locks at the Charles River Dam, near the mouth of the river at the Museum of Science.
“Because we were in a drought, they kept more water in the lower basin, versus letting more flow out” Lima said. “The consistent water level allowed the water to become stagnant. Water temperatures increased, and so it just was this kind of recipe for cyanobacteria blooms.”
Apart from the three-month-long bloom, however, the water quality in the urban part of the Charles was fairly consistent. Lima said that, had the bloom not happened, the lower basin would have earned a B.