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Boston Harbor & Rivers
February 2009
MWRA monitors water quality at more than
50 locations in Boston Harbor and its three largest tributary rivers:
the Charles River, the Mystic River, and the Neponset River. Monitoring
is conducted year-round in each region on a rotating schedule, with
the most intense sampling in spring and summer.
In general, the tributary rivers have poorer
water quality than the harbor, reflecting the impacts of urban storm runoff
and combined sewer overflows (CSOs). These three rivers are dammed near
their entry to the harbor, which reduces flushing and further concentrate
nutrients and pollutants entering the rivers from upstream.
Moderate levels of algae and water clarity
are essential to a healthy Harbor ecosystem. High fecal coliform counts
signal potential public health threats. Water quality indicators are likely
to be affected by environmental factors like temperature and rainfall
as well as discharges of contaminated stormwater or CSOs.
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THIS MONTH'S PRECIPITATION
Among other water quality indicators,
MWRA measures E. coli, Enterococcus, algae, and clarity.
Select each indicator below to view recent data from the harbor
and rivers.
E. COLI: A bacteria found in
both human and animal waste.
ENTEROCOCCUS: A bacteria that is a strong indicator of human sewage.
ALGAE: Microscopic plants, or phytoplankton, the overgrowth of which can
degrade water quality.
CLARITY: Water clarity is primarily affected by concentrations of algae and
suspended solids.
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E. COLI
E. coli is a bacteria found in human
and animal waste; it is measured in recreational waters to indicate
bacterial water quality and to assess public health risk. Counts
greater than 126 colonies per 100 milliliters of water fail to meet
the Massachusetts Department of Public Health swimming standard
and indicate poor water quality. High levels of E. coli can occur following heavy rains that carry untreated waste into
rivers and the harbor from storm runoff and combined sewer overflows.
E. coli counts greater than 126 colonies per 100 mL fail to meet
the state standard. |
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[E. Coli is no longer measured in Boston Harbor]
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RIVER E. COLI
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ENTEROCOCCUS
Enterococcus is a type of bacteria present
in the intestines of warm-blooded animals and is considered to be
an excellent indicator of human sewage. During the swimming season,
a geometric mean count above 35 colonies per 100 mL (an average
of counts from samples collected over several days or weeks) results
in prolonged closure of a swimming area. |
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HARBOR ENTEROCOCCUS
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RIVER ENTEROCOCCUS
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ALGAE
In the harbor and rivers, photosynthesis
is carried out by algae (or phytoplankton), microscopic plants suspended
in the water column. To determine the amount of algae in the water,
we measure chlorophyll. High chlorophyll concentrations indicate
an overabundance of nutrients in the water, which can result in
elevated algae levels, or algal blooms. Algal blooms can deplete
bottom-water dissolved oxygen, reduce water clarity, and impair
recreational uses. Chlorophyll concentrations greater than 12 micrograms
per liter in the Harbor and 25 micrograms per liter in the rivers
indicate an overgrowth of algae. |
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HARBOR ALGAE
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RIVER ALGAE
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| Water clarity in the harbor and the rivers
is primarily affected by concentrations of algae and suspended solids.
Secchi disks are a simple way to approximate the transparency of
water. White or black-and-white disks are lowered into the water
and the maximum depth at which they are visible is recorded. Large
secchi disk depths indicate good water clarity. Secchi disk depths
less than 1.8 meters indicate poor water clarity. |
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HARBOR CLARITY
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RIVER CLARITY
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Please address data requests or questions
about the harbor and the bay to the MWRA Environmental Quality
Department at 617-788-4601, or e-mail
us.
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