The U.S. Environmental Protection Agency said it would allow as much as 20 million cubic yards of dredged waste to be poured into an open-water dump site in eastern Long Island Sound — off Fishers Island — over the next three decades.

Beginning next month, the chosen site, 2.3 nautical miles northwest of Fishers Island, can begin to accept sand and sediment pulled from the bottom of rivers, harbors and ports — which critics say can contain mercury, lead and pesticides.

Most of the estimated 20 million cubic yards of dredged sludge will come from Connecticut’s industrialized shoreline. The designated site sits in Connecticut state waters, but it’s only 0.2 miles from New York territorial waters.

“The Long Island Sound is a shared water body, and pollution doesn’t know boundaries,” said Adrienne Esposito, executive director of Citizens Campaign for the Environment, an advocacy group based in Farmingdale. “So, let’s stop pretending that Connecticut is only going to pollute its waters.”

Harbors, ports and rivers need to be dredged to allow boats, cargo ships and passenger liners to pass safely. The contentious question is where to put the muck, and the cost of different disposal methods.

Since the 1980s, dredged waste has been dumped at four open-water disposal sites in the Sound and all four sites are in Connecticut state waters: Western Long Island Sound, Central Long Island Sound, Cornfield Shoals and New London.

advertisement | advertise on newsday

Two sites, Cornfield Shoals and New London, are scheduled to close Dec. 23, according to the EPA.

The Western and Central sites, which are expected to receive up to 53 million cubic yards of dredged material, do not have the capacity to take more. And EPA officials said these sites were too far from places that need to be dredged and would increase the distance to transport the dredged waste.

“This, in turn, would greatly increase the cost of such projects and would likely render any dredging projects too expensive to conduct,” according to the EPA.

The federal agency on Nov. 4 announced that it had selected the Eastern Long Island Sound site — 1.3 square nautical miles — despite objections from New York residents, environmentalists and elected officials, including Gov. Andrew M. Cuomo and Rep. Lee Zeldin (R-Shirley).

In August, dozens of elected officials signed a letter to President Barack Obama saying New York would sue the federal government if the EPA allowed the continued dumping of dredged sludge in the eastern region of the Sound.

“We need Gov. Cuomo to make good on his word and aggressively pursue legal action,” Esposito said.

Leo Rosales, a Cuomo spokesman, said Friday in an email that while the EPA’s chosen site was not in New York waters, the governor was concerned of the “likely” environmental impact the dumpsite would have on the health of Long Island Sound.

“The Governor has directed his legal team to continue to look at all legal options available to halt this decision,” Rosales said.