A colossal barrier with gates that open for ships has been proposed to wall off New York Harbor from the Atlantic Ocean and protect the metropolitan region from flooding as climate change increases the frequency and severity of devastating coastal storms.

The offshore barrier is one of six proposals generated by a $19 million U.S. Army Corps of Engineers study launched following Superstorm Sandy, which caused $70 billion in damage in the region in 2012. The Corps on Thursday announced three public meetings next week to explain the proposals and gather input on what issues should be addressed in the environmental impact study.

Environmental groups and politicians already are weighing in.

“The health of the Hudson River Estuary, from the Atlantic Ocean to Troy, New York, and the health and existence of its native species, depends on unrestricted tidal flow between the river and the sea,” John Lipscomb, vice president of advocacy for the environmental organization Riverkeeper, said in a statement on Friday. He said in-water barriers would restrict the flow of water and sediment and hinder the migration of striped bass, Atlantic sturgeon, herring and other species.

State Sen. Terrence Murphy, a Hudson Valley Republican, accused the Corps of fast-tracking the proposals with insufficient public notice and participation. “We know that intense storms are becoming more frequent and something must be done, but let’s put in the time and thought and have the public comment needed to make informed decisions,” Murphy said in a statement.

The Corps study references 18 structural storm barriers around the world, including the 10,000-foot-long, 26-foot-high New Orleans Inner Harbor Navigation Canal surge barrier completed by the Corps in 2013 in response to the deadly flooding from Hurricane Katrina.

The barriers proposed for New York Harbor are “conceptual,” without any details released to the public beyond dotted lines on a map. One alternative calls for a surge barrier at the mouth of the harbor from Sandy Hook, New Jersey, to Breezy Point in Queens. Others call for multiple shorter barriers — from Staten Island to Brooklyn and at various other locations blocking tributaries.

Riverkeeper said the only acceptable proposal is one that calls for shoreline-based floodwalls and levees along with beaches, dunes and waterfront parks that provide natural surge and flood protection.

In-water storm surge barriers have been proposed for New York Harbor in the past. A New York City Economic Development Corporation report in 2013 said such barriers would cost perhaps $25 billion to build, take decades to complete, cause numerous environmental problems, worsen flooding in other areas and disrupt adjacent beaches and neighborhoods.

Public meetings are scheduled Monday in New York City, Tuesday in Newark, New Jersey, and Wednesday in Poughkeepsie.

(AP)