David Lee could tell you what a bass was eating for lunch by watching the flight of swallows above a river. He knew more about bugs than Orkin and as much about the geology, plant and fish life of the upper Potomac River as anyone in the country.

So great was Lee's attention to natural detail, he probably recognized the tree that killed him.

"It's the most bizarre thing I've ever heard of," said Mark Kovach, a friend and fellow fishing guide on the Potomac River, where Lee was killed last week by a falling tree. "What are the odds of something like that happening? A million to one? I just can't imagine it."

Lee, a 41-year-old psychology professor at Hagerstown Junior College, an author of books and magazine articles and a much respected fly fishing guide, was fishing with a client on the river near Shepherdstown, W.Va., when the accident occurred. Lee and 76-year-old Edward Hollander of the District were floating in Lee's square-backed canoe, between an island and the West Virginia shore, when a large, live maple tree suddenly toppled on them.

Hollander was thrown from the canoe and suffered multiple injuries. Lee was killed by the full force of the tree trunk, which trapped him in the canoe under 3 1/2 feet of water. Rescue workers used a chain saw to cut up the tree and remove Lee's body.

"It was just a freak thing," said Lee's wife Katherine, who not only endured her husband's fishing compulsion but actively promoted it. She designed his advertising brochure and took photographs that were used in his first book, "Fly Fishing: A Beginners' Guide." "If he had been a few feet to the left, a few feet to the right, a few feet forward or back, the tree would not have hit him."

Lee was an innovative angler and a successful writer. His first book received rave reviews from a dozen newspapers, including the New York Times. He had just completed his second fishing book for Prentice-Hall and had received an advance from a Chicago publishing house to write a psychology textbook.

But he was remembered by friends at his funeral more for his curiosity than his knowledge and his kindness more than his expertise.

"Dave was a very broad-gauged guy, but he was primarily a teacher," said Dick Blalock, a retired foreign service officer who fished a day with Lee last month. "He was also the most extraordinary guide I ever met for staying out of a (client's) way. Most guides can't wait to get you out of their hair so they can fish. With Dave, all his attention was on making the trip richer for you."

Ben Schley, a retired U.S. Fish and Wildlife Service official, said Lee's only fault was his generosity with time and equipment.

"I once admired a rod of his just before leaving for a trip to Ireland. He insisted I take it with me. He was that kind of fellow."

Lee began fishing as a boy in Leesburg, Va., but did not get interested in fly fishing until he was almost 30. Once hooked, he became absorbed in the science of the sport. For the love of fly fishing for smallmouth bass, Lee lived one year in a trailer on a bank of the Potomac. "There was no heat, running water or plumbing in the trailer," he remembered recently. "Just me and my dog."

Bob Abraham, a public affairs specialist with the Maryland Department of Natural Resources, was one of Lee's first teachers. Abraham was astonished at the pace that Lee made in going from a beginner to expert.

"Dave was a tremendous reader. His interest just mushroomed. He went from being a student to a writer of books and magazine articles."

Three summers ago, Lee decided to give up teaching during summers to become a fishing guide. The venture involved some economic risks for a man with a teacher's salary and a 6-year-old daughter. But Lee was prepared to lose money to do something he loved.

"Right now we'd probably be discussing medieval witchcraft and phrenology," Lee told me during a fishing trip last July. "It's a good course but I've already taught it 120 times."

In my notes from that trip I recorded seeing wood ducks, herons and the remains of old Indian fish traps. What I remember most from that day, however, is conversation. We talked about contemporary literature, Jungian psychology and Andrew Jackson. More interesting to me were his observations about the appeal of fishing.

"Fly fishing has layers of complexity just like an onion. Most people I take out like things to be complex," said Lee as we floated down the same stretch of river where he would die a year later. "One thing people always insist on in their sport is failure."