An 11-block portion of Rockaway Beach will be closed this summer due to erosion and for maintenance of a protective dune — cutting off visitors from a chunk of the beach just before it was to open for the season on Memorial Day weekend.

The city parks department announced Monday that the area between Beach 91st St. and Beach 102nd St. will be closed during the summer season. Officials said the dune, which was built after Hurricane Sandy, is in that portion of the beach.

Beach season runs from Memorial Day weekend until Labor Day, after which point city beaches will be closed to the public again.

Parks officials said the erosion had whittled down the beach to the point that there is not enough space for people to safely go through it or safely swim in the water.

Speaking to NY1's "Inside City Hall" on Monday night, Mayor Bill de Blasio said the stretch that will be closed would be particularly narrow during high tide and would not be safe for beach visitors.

Part of the beach in front of the concession stand and bathrooms at 97th St. will remain open, but people will not be allowed to enter the water.

About 4.5 miles of the beach will stay open, along with the boardwalk and the surfing area from Beach 88th St. to Beach 91st St.

The Rockaway Boardwalk fully reopened last May after it had been shut down for repairs in the wake of Hurricane Sandy.

Queens Borough President Melinda Katz called the decision "unacceptable," saying preventing people from visiting parts of the beach will shortchange the borough's economy.

Rockaway residents had previously called on the city to address increasing erosion along local beaches.

Katz said they sounded the alarm in 2014 when the Army Corps of Engineers last replaced 3.5 million cubic yards of sand on the beaches, arguing that sand would need to be replaced again.

"The consequences of the City's failure to act earlier will be disproportionately borne by the Rockaway community," Katz said in a statement.

De Blasio said the Army Corps of Engineers agreed to expedite the restoration process for the closed portion of the beach and provide long-term solutions. A timeline for that process is expected over the next few months. The mayor said the restoration is only practical with their help.