Amerique, an 8-year-old Thoroughbred who has won more than $400,000 in his racing career, is ready for his morning workout. With a clatter of hooves he makes his way into Roger Collins's Middleburg, Va., training center. Then he starts swimming.

Collins has operated the pool—officially the Northern Virginia Animal Swim Center—for hunters and racehorses since 1989, when he and his wife, Laura Hayward, bought the 43-acre farm smack-dab in Virginia's horse country. The pool was already in place, if a little decrepit, so Collins, a 56-year-old London native who has two horses of his own, decided to try to make it a going business. The result: Each week some 100 equine aquacisers get water workouts—at $12 a dip. "Swimming is good for the lungs and heart and better than being on hard ground," says trainer Don Yovanovich, who works out horses in the pool daily.

While there are a handful of other horse pools across the nation, most are for rehabilitating injured animals. Not so Collins's pool. "The majority of the horses here swim for conditioning," says Collins, an executive for the Red Cross in Gaithersburg, Md. "We use swimming as a way to get horses fit."

For Amerique, that means 10 turns of the 30-by-50-ft. pool, followed by a hosing down. Then it's off to his dry-land training regimen—but no sauna, no steam room and no Jacuzzi.