Brad Pitt trained himself to fly-fish for four weeks before shooting. Since he was not near any river in Los Angeles, he trained on top of a building.
Norman Maclean often recounted the story of how his semi-autobiographical story collection was rejected by every large commercial publisher he sent it to, including one that rejected it on the basis that it contained "too many trees". It was eventually published instead by the University of Chicago Press (in 1976) and went on to sell extraordinarily well for them.
Robert Redford courted author Norman Maclean for years to gain the rights to his autobiographical novella.
George Croonenberghs was a retired railroad engineer. He taught Brad Pitt, Craig Sheffer and Tom Skerritt how to fly-fish for this movie. He also taught fly-fishing and fly-tying to his fellow residents, and staff members, of his retirement community. He grew up near the Maclean family in Missoula, Montana. His family's cabin was built next door to the Maclean family cabin in Seeley Lake, Montana. He learned to fly-fish and tie flies from Rev. John Maclean, and considered Paul Maclean to be his best friend. The friendship between the Maclean and Croonenberghs families continues to this day, into its fourth generation.