Three quarters of a million beachgoers crammed the Coney Island Boardwalk Saturday for an air show, but syringes and blood vials washing ashore kept swimmers out of the water as temperatures climbed toward the 90s.

Tide-borne medical debris also washed up on Brighton Beach, forcing Parks Department officials to hoist red "no-swimming" flags there and at Coney Island, bringing to at least 13 the number of New York-area beaches closed by pollution.Good water quality was reported at most other New York and New Jersey beaches.

The Green Beret Precision Parachute Jump Team leaped from an Army helicopter in the early afternoon, prompting cheers and sighs from the huge crowd as the soldiers spiraled earthward, their gray canopies silhouetted against the sky and their ankles trailing streams of red smoke.

An Air Force F-16 screamed overhead, twisting and turning in a jet acrobatic demonstration.

Milton Berger, the air show chairman, said 750,000 people crowded onto the popular boardwalk and beach for the show.

But disappointed beachgoers were ordered to stay clear of the water as the Coney Island Beach was closed during a sweltering weekend. The beach was closed briefly earlier this summer when a power outage knocked out a Staten Island sewage treatment plant and officials feared raw sewage would wash ashore.

"Workers inspecting the beaches this morning found three syringes and two blood vials and based on that we decided to close Coney Island beach and Brighton Beach," said Colette Beaudry of the city Parks Department.