Three people were killed and four others seriously injured when their 40-foot powerboat plowed onto marshland on a moonlit Sunday night off Long Island's southern shore, authorities said.

The Hustler speedboat was navigating a channel in an area dotted with boggy salt marshes, just south of Wantagh, when it ran aground, authorities said. The boat's captain was thrown off the craft, and pronounced dead by rescuers when they arrived.

Capt. Joe Frohnhoefer, the founder of SeaTow, a marine assistance organization with headquarters in Southold, said one of its boats was the first to arrive at the crash site, near Wantagh Parkway that leads south to Jones Beach. He said the lone crew member found four people injured and one dead. The boat was about 150 feet from the water, Frohnhoefer said.

"To hit the marsh and run up on top of it like that, you would have to be going at a pretty good rate of speed," Nassau County police Det. Lt. Kevin Smith told Newsday in Monday editions.

Smith said he did not know how fast the boat was going.

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The Nassau County Police Department said officers responded about 7 p.m. to the accident, along with the U.S. Coast Guard, Wantagh Fire Department and the New York City Police Department. At least two people were airlifted to nearby hospitals, according to the Coast Guard.

The survivors remained hospitalized early Monday.

Nassau County police were investigating the cause of the accident. They did not release the names of the victims.

Frohnhoefer said he wasn't surprised by the crash, adding that he has seen four similar accidents, where boats run up usually on sandbars while trying to navigate the complex network of channels and bays.

"It's a lack of knowledge, a lack of boating knowledge," he said.

Frohnhoefer said the speedboat that crashed was built for racing.

Hustler, the Calverton, N.Y.-based company that built the boat, has a model capable of reaching speeds over 150 mph.