A Pennsylvania woman who was driving a sport utility vehicle carrying three people that fell off the Chappaquiddick ferry and into the Edgartown harbor last week has been cited by police for negligent operation of a motor vehicle and operating under the influence of alcohol.

Susan McLean, 54, of Ambler, Pa., was issued a citation by Edgartown police last Thursday evening. She has since requested a show cause hearing in front of the Edgartown district court clerk magistrate. The date of the hearing is kept confidential.

Ms. McLean was behind the wheel of a 2006 Mercedes-Benz sport utility vehicle along with two passengers — her daughter, Audrey McLean, 19, also of Ambler, Pa., and Alexander Tasch, 23 of Nantucket — when it fell off the Chappy ferry and into the harbor on March 25.

The accident prompted a hasty rescue of the occupants and the vehicle.

The captain of the ferry, Brad Fligor, reportedly hauled the three people out of the water and onto the ferry and called 911 for assistance. A large number of police, firefighters, emergency medical technicians, divers and other rescue personnel responded to the scene and worked for several hours to haul the sport utility vehicle out of the water.

All three passengers were out of the water by the time emergency personnel arrived, police said.

Both Susan and Audrey McLean refused medical treatment at the scene, while Mr. Tasch was transported to the Martha’s Vineyard Hospital where he was treated for minor injuries and later released.

The mishap took place during the final trip of the Chappy ferry for the evening around 11 p.m. Police reports indicated Ms. McLean was moving the steering wheel back and forth and pretending to drive the ferry, causing the wheel to knock aside the wooden chocks that normally hold the vehicle in place.

The police report also said Ms. McLean admitted to having two glasses of wine at an Edgartown restaurant, and exhibited clues of a blood alcohol level higher than .10 during a field sobriety test. Police also detected a moderate odor of alcohol inside the vehicle, the report says.

The driver disputes some of the information in the police report.

The incident is under investigation by the U.S. Coast Guard.

Meanwhile, this week Captain Fligor and ferry owner Peter Wells appeared before the Edgartown selectmen to explain the incident, where they drew praise.

“Want to express our thanks to [Mr.] Fligor . . . your actions averted what could have been a different story,” selectman Margaret Serpa said.

“You guys did a great job,” agreed chairman Michael Donaroma.

Mr. Fligor credited Mr. Tasch, who reportedly rolled down a window before the car completely submerged, for making it easier to open the doors and extricate the passengers.

“I’d like to thank the passenger in the vehicle; he rolled his window down before the electric went out . . . otherwise it would have been a different story. Thank God there weren’t any injuries,” Mr. Fligor said.

Reached by telephone this week, Mr. Wells said there was little he could say about the incident while the Coast Guard investigation continues. He did commend Mr. Fligor for acting quickly to help pull the three people out of the harbor.

Although unusual, a vehicle falling off the Chappy ferry is not unprecedented.

Perhaps the most memorable incident occurred in September of 1950, when a volunteer firefighter was seriously injured when the new fire truck valued at $12,000 — a substantial sum at the time — slid backwards off the On Time ferry and into the water.

The fire truck was headed to Chappaquiddick to battle a fast-moving brush fire that eventually destroyed five buildings on a single property: a carpentry shop, a tool shed and three barns, as well as 550 baby chickens. There was speculation at the time that the new fire truck could have prevented much of the damage if it hadn’t fallen into the harbor.

A report in the Gazette at the time said the truck fell off the ferry after its front wheels started up the ramp and the power of the rear wheels pushed the scow away from the shore, causing the securing chains to snap. The rear end of the truck then went into the water. A volunteer firefighter was pinned against one of the ferry’s chains.

In June of 1958, a truckload of lumber bound for Chappaquiddick fell off a truck and nearly caused the scow to go under. The truck stalled just before getting onto the ferry, before it could be centered for a smooth passage. The sudden tilt caused a shifting of the weight of the lumber and the chains confining the wood broke, causing the planks to slide off the truck and over the side of the scow.

In a similar incident, a dump truck loaded with 14 tons of lime headed for Pimpneymouse Farm on Chappaquiddick nearly capsized the scow in April of 1966. The ferry master noticed the heavy load was not centered and asked the driver to back off and come aboard again, more to the left.

A story in the Gazette explained what happened next.

“Just as the truck started back up the gangplank, something happened, no one is sure exactly what. Perhaps the wheels spun on the wet dock, or perhaps a sharp turn of the front wheels cause the truck to skid. At any rate, the truck suddenly lurched aft and to the left, its rear wheels departing overboard while its heavy top canted violently to the right where the capping rail of the town dock prevented it from toppling overboard.

“All this weight on the right edge of the ferry shot her bow up in the air and her stern came down on the harbor bottom.”

Gazette reporter Sam Bungey contributed to this story.