A Brooklyn native died yesterday morning during a grueling swimming competition across the East River, authorities said.

Richard Harley, 59, who made his residence in San Rafael, Calif., suffered a heart attack while swimming between Manhattan’s South Street and Brooklyn Bridge Park as part of the annual Brooklyn Bridge Swim, sources said.

He became distressed as he trudged under the bridge less than five minutes into the 9:45 a.m. event, said Morty Berger, founder of NYC Swim.