(FORTUNE Magazine) – America's lakes, rivers, and streams are thick with them: swarms of fly- fishermen. In ever-increasing numbers, they read the river, match the hatch, and cast furry hooks with bug-lauding names like green drake wulff, yellow humpy, and pale evening dun. For most, fly-fishing is less an art than an exercise in frustration. But the sport's attractions -- beautiful natural settings, technical challenges, and elite status -- are making it a popular piscatorial pastime for baby-boomers. Fly-fishing schools and classes around the U.S. are netting record numbers of applications. L.L. Bean, which operates a school near its store in Freeport, Maine, has expanded its $325 three-day sessions to 17 this year from ten a year ago. Orvis reckons it will educate up to 1,200 people this year at its fly-fishing academy in Manchester, Vermont, where classes cost $320 for 2 1/2 days. Last year it taught about 1,000 people and turned away 300 more. Frontiers International Travel, located in Wexford, Pennsylvania, expects to take more than 3,500 trout seekers to places like Alaska, Patagonia, and the Yucatan. ''In the past, the only people who could afford these trips were in their middle 50s and older, the CEOs,'' says Silvio Calabi, editor of Fly- Tackle Dealer magazine. Now, he says, the clientele is changing: ''I met a group on their way to Patagonia. There was a rock music producer, a buyer for Bloomingdale's, a writer, and a couple with 'trust fund' stamped on their foreheads -- all very nice people.''