A small, glass-enclosed tour boat tipped over yesterday in the calm, cool waters of Lake George in Upstate New York, killing at least 21 people, most of them senior citizens.

The Ethan Allen, a 40-foot-long craft, was plying a one-hour, narrated loop along the west side of the lake about 2:50 p.m. when it apparently hit the wake of another ship. The Ethan Allen, witnesses said, wobbled and then swamped about 150 yards offshore, spilling its 49 passengers into the water.

Some passengers apparently became caught under the boat, while others struggled -- with broken ribs and bleeding cuts -- to stay afloat.

But for some, rescue efforts were to little avail. A number of the passengers relied on walkers and wheelchairs to get around, the Albany Times Union reported.

"They are on in years, and the shock seems to have put a number of them into cardiac arrest," said John Santiago, owner of the Diamond Cove Cottages. "They couldn't take it."

A spokesman for the American Red Cross said last night that at least 21 passengers were confirmed dead. Many of the survivors were taken to nearby Glens Falls Hospital, and seven were admitted, a hospital spokesman said.

Officials and area residents said most passengers were from Michigan. Fourteen were from Trenton, near Detroit, Trenton Mayor Gerald Brown told WJBK-TV in Detroit, saying that at least three were killed.

Brown said the group left Tuesday on a weeklong bus-and-rail trip to see changing fall colors along the East Coast. The trip was organized through the city's parks and recreation department and arranged through a Canadian company. At least some of the surviving boat passengers are French speakers, and a Red Cross spokesman said the agency was bringing in interpreters.

The National Transportation Safety Board and the Coast Guard will begin an investigation of the accident today.

The boat had life vests, but few, if any, passengers were wearing them, witnesses said. It was a beautiful autumn day, and the lake temperature hovered around 68 degrees.

Frank Sause was returning from church when he saw ambulances caterwauling down his road. He drove to the lake's edge and began helping elderly people out of the water.

"One man said to me, 'I just saw them pull my wife out of the water, and she was dead,' " recalled Sause, who owns cottages along the lake. "I tried to tell him not to jump to conclusions, but you could see the rows of bodies with white sheets pulled over.

"That," Sause added, "is when I realized that people were dying out there."

Three dozen private and emergency police boats came immediately to the scene, and some boaters tossed life preservers to those in the water while others hauled in passengers and administered cardiopulmonary resuscitation.

Residents waded into the water to help the passengers to shore. Scuba rescue teams arrived within 25 minutes and repeatedly plunged beneath the waters off Cramer's Point.

The Ethan Allen now rests on the lake bottom, about 75 feet down. The ship's captain and only crewman, Richard Paris, survived.

The accident, as described in preliminary police reports and by area residents, sounded like a fluke. The Ethan Allen, a low-slung boat, was making a turn to head back down the western shore of the lake, and passengers were shifting from one side of the boat to the other. Police are investigating whether at that moment the wake from a much larger, century-old cruise boat, the Mohican, may have washed against the smaller ship.

"It was just weird circumstances," Sause said.

The owners of the two cruise ship companies -- Shoreline Entertainment, which owns the Ethan Allen, and Lake George Steamboat Co., which owns the Mohican -- were not available for comment. The boat's owner, Jim Quirk, whose family has operated Shoreline Cruises for decades, told the Glens Falls Post-Star: "It is a tragedy, and it's very unfortunate."

Lake George, which is 32 miles long and 200 feet deep, has long been a resort destination, its clear waters and southern Adirondack peaks attracting tens of thousands from New York City and Albany. The road that runs along the shore near the boat accident was once known as Millionaires Row.

Besides the summer, this is one of the busiest times of the year in Lake George, as the autumn colors attract tourists from across North America.

By Cramer's Point, though, the mood was funereal last night, as police divers put away their equipment, and police and rescue crews loaded bodies wrapped in sheets into ambulances and hearses.

Garcia reported from Glens Falls, N.Y.

Brian Hart of East Greenbush, N.Y., is thanked by one of the women he saved when a tour boat carrying mostly elderly passengers tipped on Lake George.