Con Edison says they have recovered nearly 600 gallons of oil from the East River following a spill earlier this week.
Officials also say samples of the water have tested positive for PCB, a known carcinogen.
The agency is advising people not to eat any fish or shellfish from the river.
The Coast Guard has also banned recreational boats from the area.
On Sunday afternoon, a transformer at one of Con Ed's Brooklyn sub-stations failed, causing 31,000 gallons of oil to spill into the East River.
The agency said it is working with the Coast Guard, the state Department of Environmental Conservation (DEC), and other agencies on the cleanup.
The DEC is investigating the spill.