Major beaches in New York City and Long Island reopened for swimming Saturday as officials were pressed to determine whether medical debris found along the shore came from boardwalk junkies or careless sewage disposal.

Officials closed vast stretches of the Atlantic shore during last week's heat wave after beachgoers reported finding dirty syringes and vials of what appeared to be blood washing up on the bleach-white sand."We are still looking at the matter that has washed ashore from the last three days and we will trace what we can," said Madeline Lewis, a spokeswoman for the state Department of Environmental Conservation.

Investigators were doubting an earlier theory the medical debris originated at a hospital, she said.

"It looks like waste from a sewer overflow or boat debris," she said.

New York City Parks Commissioner Henry Stern declared the 14.9 miles of city shoreline safe after an early morning dip off Far Rockaway, a city beach that was closed Friday.

Stern blamed drug abusers for the six syringes found along city shores.

"We have inspected the debris collected over the last several days and have concluded that it was not waterborne," he said. "There were syringes that were found but we believe they were discarded by local junkies rather than washed ashore as medical waste."

"The beach looks normal and the water feels great," he added.

But Lewis said she believed the syringes discovered on Long Island's beaches probably came from the water, although it was unlikely the debris originated from illegal dumping from a garbage barge.