Oyster Overview

Oyster Benefits

Oysters provide many benefits for the water and the sea life in an area:

They filter water in rivers and tidal estuaries: 30 gallons per oyster per day
Feed on phytoplankton and silt
Improve water clarity
Control algae and capture nitrogen and other bacteria
Offset the impact from sewer overflows and other manmade pollutants
Cleaner water attracts other sea life such as sea bass and crustaceans

Oysters may be able to offset point pollution sources such as partially treated sewage coming out from Combined Sewage Overflows (CSOs). The number, flow, and impact of these has been reduced dramatically by the fine work of the MWRA. But it will be difficult to totally eliminate CSOs entirely. The following diagram shows how these overflow during dry and wet weather conditions:

There still is considerable CSO flow entering the harbor, as seen in the map below (click on map for full view):

Source: MWRA Recommended CSO Control Plan and Report 2005

Oyster Demise

Oysters were once abundant in the Boston Area:

Neponset, Mystic and Charles Rivers all had abundant beds.
Back bay reef may have served as food source for the poor.
Very popular food source for native Americans, colonial times and up through 20th century

However, oysters are no longer present in the Charles or Mystic. Many reasons contributeto their demise:

Misuse: Oyster shells and sometimes whole oysters were harvested to spread on fields to reduce soil acidity
Pollution: sewage flows, river silt, chemicals. At one time the lower Charles had 75 mills.
Overharvesting: feeding humans
Loss of habitat: through fill
Protective dams convert significant areas of Back Bay and Mystic Rivers to fresh water.

The following map shows the how much the oysters' habitat has changed over the last few centuries. The yellowline represents the shoreline in 1630. Note the extensive filling of the Back Bay. Salt water once extendedall the way to Watertown.