A proposal to connect the New England and New York power grids earned final regulatory approval this past week, but opponents vow to continue fighting the project.

On March 19, the U.S. Army Corps of Engineers approved Cross Sound Cable Company’s application to place an electric cable in the Long Island Sound seabed. Work on laying the cable, which will run from New Haven to Brookhaven, N.Y., on Long Island, could begin as soon as April 1.

“We have concluded that the proposed project will not impact the operation and maintenance of the federal navigation channel in New Haven Harbor, and have minimal impact on the marine environment,” said Col. Brian Osterndorf, district engineer of the New England District.

But Connecticut Attorney General Richard Blumenthal said in a March 20 statement that he would file for an immediate injunction in Superior Court to stop the cable’s construction.

“I am deeply disappointed by this decision, which approves a project so clearly anti-consumer and anti-environment,” Blumenthal said.

New Haven Mayor John DeStefano Jr. and the New Haven Board of Aldermen also strongly oppose the cable project.

The high-voltage direct current and fiber optic cable system would run for 24 miles in the seabed, roughly 6 feet below ground in the navigation channel and 4 feet deep elsewhere. The cable would have the capability to transmit in both directions, but Cross Sound Cable already has an agreement to provide power to Long Island.

Challengers to the cable say its operation would tax Connecticut for New York’s poor energy planning. The larger energy market also would increase utility rates as local power stations produce more electricity to send to Long Island. In addition, the cable’s electric and magnetic fields could pose environmental concerns to sea life.

The Corps issued its permit with 23 special conditions for Cross Sound Cable, but Blumenthal feels the restrictions do not go far enough.

“Even with the conditions the Army Corps plans to place on the project, it will do damage to consumers and our environment that is severe, immediate, and irreparable,” Blumenthal said. “It promises higher energy prices, disruption and destruction of the Long Island Sound environment, and damage to our state economy.”

The special conditions were not available in the Corps’ initial report.

The project’s opponents also fear that the cable’s placement in New Haven’s federal navigation channel would prevent future dredging to allow large ships to enter New Haven Harbor. But the Corps believes the 6-foot depth will provide ample room for future expansion.

“We are requiring a depth that will include enough room for a possible future deepening of the channel if that were to be authorized and funded,” Osterndorf said.

Cross Sound Cable must also issue $1 million in bonds to provide funds if the cable must ever be removed or require emergency repairs.

On Jan. 3, the Connecticut Siting Council unanimously approved the project, 8-0. The council had previously rejected an alternative route of the cable by a 7-1 vote last March because the cable could have harmed shellfish beds. The Connecticut Department of Environmental Protection issued Cross Sound Cable a permit earlier in March.

The Corps had never approved a cable or pipeline in a federal navigation channel before. The decision could set a precedent for additional pending applications, such as a gas pipeline in Boston.