The plants discharge what is funneled to them through the sewers.
The city also said that the plant is discharging pollutants like oil and grease in violation of permits.
During Grand Jury testimony, one witness estimated that the plant discharged waste through the pipe for 330 days out of 365.
Forty-four sewage-treatment plants discharge into the Sound, and 14.6 million people live within the area that drains into it.
Its plants discharge more than half the 1.1 billion gallons of treated waste water that flow into the sound every day.
Ultimately, the plants discharge the toxics into the city's waterways, making them a leading polluter.
As of last year, more than 80 sewage-treatment plants discharged into tributaries that led to reservoirs.
The plant discharges about 750,000 gallons daily but holds a state permit for 1.2 million gallons.
Yet even when the plant discharged 372,000 gallons per minute of warmer water, the fish didn't seem to mind.
As a result, the plant discharged its own improperly treated waste into the Nemasket River.