His wife, Martha Poole Merwin, who confirmed his death, said he had been hospitalized recently with several illnesses.

Mr. Merwin was 3 and living in a converted mill house on his grandfather's farm in Wilton, Conn., when he first cast a line into water. More than 60 years later at a lakeside inn in New England with his wife, he planned their days around bass and bluegills.

"Right after we check in, I mosey into the dining room," he recalled in a 2011 article in Field & Stream. "Breakfast comes out at 6 a.m. and dinner service stops at 10 p.m., which means we can fish early and late, the best times for summer bass, without missing a meal. Perfect."

Mr. Merwin spent his life tying flies on lines and taking measure of morning sun on marshes. He fished and worked with masters, including Lee Wulff and A. J. McClane, who helped elevate fishing to a high-minded obsession, but he was also quick with tips for beginners. His casts with a fly rod were the envy of other anglers, but he insisted that casting a spinning reel was no less noble.

"When I was too much on the high horse of fly fishing, he'd send me a picture of him holding a big trout and a spinning lure hanging out of its mouth," said Kirk Deeter, the editor of Trout magazine and an editor at large at Field & Stream.

Mr. Merwin could be gruff and critical and warm and patient. Always, everywhere, he fished. He had a map of North America in which he put tacks in places he had traveled.

"We got tired of putting in all the pins," his wife said.

He fished on (and off) other continents, too, including Europe and South America. Mr. Deeter said, "You have to fish a lot in order to write about fishing with credibility."

After working as a newspaper reporter, Mr. Merwin was trying to make a living farming in Vermont in the 1970s when he decided he could write better articles than those he read in Fly Fisherman magazine. He eventually moved to Dorset, where the magazine was based, and became its managing editor.

By the late '70s he had founded Rod & Reel magazine, which later became Fly Rod & Reel. He also started Fly Tackle Dealer, the industry's first trade magazine. He joined Field & Stream in 1994 and became its fishing editor in 2003. He retired from that position in 2010 but continued to write articles and blog posts.

Mr. Merwin wrote many critically praised books, including "Stillwater Trout" and "Fly Fishing: A Trailside Guide." In 1994, he wrote "The New American Trout Fishing," which many outdoors writers consider a classic.

"The big complaint from some writers in popular outdoor literature is that they used to be able to write stories and now they have to write cookie-cutter how-to pieces," said Dave Hurteau, a deputy editor at Field & Stream. "John was in the middle of that transition. He was smart enough to combine them in 'The New American Trout Fishing.' He knew exactly what he was doing."

John Henry Merwin was born on Nov. 9, 1946, in Norwalk, Conn. Part of the farm in Wilton where he grew up is now Merwin Meadows Park. Mr. Merwin studied fisheries management at the University of Michigan but did not graduate.

In addition to his wife, survivors include a daughter, Emily; two sons, Jason and Sam; a granddaughter; and two brothers, Tom and Gus.

Mr. Hurteau said that what struck him most about Mr. Merwin was not any particular accomplishment but his passion.

"I love fishing, but I could never love it as much as John does," he said. "Nobody could milk the simple pleasure of catching a fish like Merwin."

This article has been revised to reflect the following correction:

Correction: February 27, 2013

An earlier version of this obituary misstated the name of Mr. Merwin's daughter. She is Emily, not Cassandra, who is Mr. Merwin's granddaughter.