CHINCOTEAGUE, VA., JULY 25 -- Animal-rights activists kept watch today as about 150 wild ponies made the 65th annual Chincoteague Island pony swim across Assateague Channel.

A crowd of about 40,000 people, including the activists, saw the ponies complete the 10- to 15-minute swim about 1 p.m. The ponies swim the quarter-mile channel at slack tide, the time between high and low tide when the current is calm.

Bonnie Scribner, of Voice for Animals, a Charlottesville-based group, said after watching the swim that she "had seen nothing amiss. But the swim is just part of it," she said. "We don't approve of the sale of foals under 4 months of age."

She said last year there was no veterinarian available and two ponies died. Her organization came to make sure a veterinarian was present. There were two on duty, and Scribner said she was delighted.

Gail Eisnitz, of the Humane Society of the United States, said the event is "real stressful for the horses and ponies. We feel it is animal exploitation for human entertainment and for big bucks."

Some of the foals will be sold at auction Thursday by the fire department to control the herd size. Last year, the department made $40,000 on the sale of 77 foals.

Ed Moran, president of the Chincoteague volunteer fire department, said all the money raised, including that from a $25 video of the swim, goes "back into the community." He said it pays for maintaining the department's three firetrucks and four ambulances.

About 20 to 25 people wilted in the midday heat and were treated at Island Medical Center, said ambulance chairman Ollie Reed.

The animals are thought to be the descendants of ponies that washed ashore during Colonial times from shipwrecks. The ponies gained fame from Marguerite Henry's children's classic "Misty of Chincoteague," published in 1947.

The Humane Society of the United States has been monitoring the annual event for 20 years.

Eisnitz said conditions for the animals have improved. But in the past two years, six animals have died.

As a result of those deaths, the Chincoteague National Wildlife Refuge on Assateague threatened to revoke the fire department's permit to graze the animals on the refuge if the department did not provide a veterinarian for the swim, penning and auction.

Eisnitz said the federal government has demanded improvements in exchange for the grazing rights.

"The fire department has enlarged the corral, provided a shaded area and more water for the animals. They have also cut back the chokecherry bushes," she said.

"I think they enjoy it," Everett Lewis, a 15-year veteran of the fire department, said of the ponies. "It seems like they've learned this over the years."