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Boston-area water quality report cards show widespread improvement, but still range from A to F

A pair of paddle boarders headed up the Charles River while taking in the view of Boston’s skyline.Nathan Klima for The Boston Globe/The Boston Globe

Newly-released report cards on water quality in three Boston-area rivers showed top marks for main portions of each watershed, pointing to widespread improvement in bacteria concentrations, but poor grades in several smaller segments reveal where localized challenges remain.

The US Environmental Protection Agency released its 2020 water quality report card for the Charles River, Neponset River, and Mystic River on Wednesday, the first time all three watershed organizations collaborated with the EPA on their grading calculations. The three watersheds make up a significant portion of the fresh water that makes its way into Boston Harbor, and all three have an impact on the harbor’s water quality, according to the EPA.


The grading systems are based on the percentage of time bacterial levels in the water meet swimming and boating standards during both wet- and dry-weather events. The data show that bacteria concentrations tend to be lower in dry weather, and much higher during or after rainstorms. The data also show that boating standards are often met throughout each watershed, but swimming standards are less likely to be met, especially when the weather is wet.

The report said among the main problems remaining were sewage discharges into waterways during heavy rainfall when sewers became overwhelmed, though it noted such discharges have been reduced by about 87 percent since the 1985. The report also cited cyanobacterial blooms, which are caused in part by excess phosphorus washing into the watershed from lawns, roofs, and streets — an increasingly common phenomenon.

All three watershed organizations credit the work of citizen scientist volunteers who help collect monthly water quality samples throughout each river.

The three grading systems use a three-year rolling average, “which helps account for interannual variation in the weather,” according to the EPA report. Here’s a look at how each watershed performed.


Neponset River

In the Neponset watershed, the report shows that most segments rated in the “A” or “B” range, with smaller tributaries and ponds receiving grades in the “D” to F” range, including Unquity Brook, Purgatory Brook, Germany Brook, and Meadow Brook. The river’s lower segment received a “B-” grade and its upper section was given a “B.”

In addition to grades for bacteria, the Neponset watershed association also measures phosphorus and dissolved oxygen, “which are important for fish and wildlife, as well as recreation,” the EPA said.

“By continuing to find and fix sewer defects, and by working with private and municipal partners to solve the big challenge of polluted rain runoff from roads and parking lots, we will make the river an even more valuable resource for recreation and fish and wildlife in all our communities, including our environmental justice neighborhoods,” said Ian Cooke, executive director of the Neponset River Watershed Association.

This year marked the first time Neponset recorded grades for streams throughout the watershed.

Mystic River

The main segments of the Mystic River received grades in the “A” or “B” range, while the report flunked several other smaller segments throughout the watershed, including Mill Creek in Chelsea, while Winns Brook in Belmont received a “D-” grade. The river’s fresh water segment received a “B+” and its salt water segment got a slightly lower “B” rating.

“The good news is that the Mystic — like each of the three great rivers of Boston Harbor — is a relatively clean urban river, safe and accessible for a variety of recreation,” said Patrick Herron, executive director of the Mystic River Watershed Association. “But there is still work to be done, and the report card we publish with EPA’s collaboration shows where effort should be directed on the ground.”


Charles River

Following similar trends from past years, the report shows that five out of the Charles River’s six segments were graded in the “A” to “B” range, with one section, the Muddy River in Boston, receiving a “D-” score. The river’s middle basin received an “A-” and its lower basin received a “B-” rating.

“The wide variety in Charles River grades from an A in the middle watershed to the D- in the Muddy River reflect the predominant land use around each area,” said Emily Norton, executive director of the Charles River Water Association. “Areas with more development and impervious surface are more polluted. We have work to do to restore all areas of the Charles to be ecologically healthy.”

According to the report, the EPA has taken additional actions to address elevated nutrient levels throughout the Charles. Last year, the EPA began gathering input about how to address storm water runoff from commercial, industrial, institutional, and residential properties surrounding the river that are not currently regulated.

“EPA is currently evaluating that input along with existing data and expects to make a decision by the end of the year,” the report said. The hope that a similar approach would work in both the Mystic and Neponset watersheds, the report said.


Brittany Bowker can be reached at brittany.bowker@globe.com. Follow her on Twitter @brittbowker and on Instagram @brittbowker.