After a long Fourth of July weekend in the Hamptons, a 75-year-old woman and her 16-year-old granddaughter were enjoying a smooth seaplane ride back to Manhattan — until the last 15 seconds.

That’s when the 10-seat aircraft suddenly crashed into the East River, tipping to one side, its wing submerged.

They were rescued from the choppy waters along with four other passengers, a pilot and a crew member on Sunday, according to Fire Department officials and interviews with the woman, Ada Todd, and her granddaughter, Khloe Todd, who captured cellphone footage of the crash.

“I wanted her to have an experience, but this experience was very bad,” said Ms. Todd, who had traveled in seaplanes before. “Thank God we’re alive.”

None of the passengers were seriously hurt, the officials said. Ms. Todd said her head throbbed and her back ached.

The plane made a hard landing, causing a wing strut — a support brace that attaches to the fuselage — to snap, according to the Federal Aviation Administration, which is investigating the incident.

The plane, which left from East Hampton around 11:15 a.m., was heading to the seaplane base Skyport at East 23rd Street and Franklin D. Roosevelt Drive around noon when it struck a wave while landing, causing the aircraft to partially capsize, fire officials and the police said.

The plane jolted, violently, as it touched down, the footage shows. The pilot called out, “Mayday, mayday, mayday,” as the aircraft’s instruments began to beep.

Several people gasped, the footage shows. Ms. Todd gripped the seat in front of her. “What happened?” she said, panicked.

Within 90 seconds, Fire Department and police boats pulled up to the plane.

“Without them, I don’t even know how it would have gone out there,” Khloe said. “The way they responded so quickly, that saved us big time.”

Onlookers saw the crash from Manhattan’s waterfront. Marcus Hurlburt, 39, said he was running along the East River about a block away, near East 22nd Street, when he saw the plane approach the landing zone and clip the water with its left wing.

“The pilot did a great job on making sure it didn’t turn over,” he said.

“He pulled a Sully on that one,” he added, referring to the pilot Chesley B. Sullenberger III, who landed a commercial jet in the Hudson River in 2009, saving all 155 people on board. “I was so impressed the pilot didn’t let it sink.”

Mr. Hurlburt said he saw least three people who were aboard climb onto one of the plane’s floats, opposite the submerged wing. He watched, he said, as the wing appeared to sink deeper into the water.

But he said Police Department and Fire Department boats, as well as another seaplane that had already landed in the water, arrived soon after the landing to transport the passengers back to shore.

“They all responded within minutes — very, very quickly,” he said.

Ms. Todd, who lives in Manhattan, and Khloe, from Fort Lee, N.J., had been driven to East Hampton, a fashionable town on Long Island, about 100 miles from Manhattan, where celebrities and New York socialites often vacation in the summer months.

“We were like: ‘Let’s not drive home. Why don’t we take a seaplane? Let’s experience it,’” Khloe said.

The first indication that something was amiss was when the pilot attempted to land but lifted off again, she said. He then circled around and made another attempt.

“It went down from there,” she said. “All you heard was ‘boom, boom!”

The owner of the 10-seat plane, a Kodiak 100, requested that their identity not appear in public databases, and its flight routes are not publicly available, according to its F.A.A. registration profile and FlightAware, a plane-tracking website.

Ms. Todd and her granddaughter bought their tickets from Blade, a helicopter charter company. A spokesman for Blade said: “A seaplane operated by Acadian Seaplanes made a hard landing on the East River. All passengers and crew are safe, and passengers were provided transportation to their destinations.”

Acadian Seaplanes could not immediately be reached for comment.

It is not uncommon for aircraft to crash in New York waters. Last month, a small plane crashed into the East River near the Throgs Neck Bridge in Queens. No injuries were reported at the time.