The first day Robert Hawkins fished on Lake Mille Lacs, the only fish he caught was a 57-inch muskie, landed on a fly rod — a possible world record.

Hawkins, a Minnesota transplant who came from Montana, set out on Mille Lacs on Monday at daybreak, accompanied by two pals.

About 10:30 that morning, after casting a custom-made foot-long fly into about 10 feet of water, he hooked his muskie, a monster estimated to weigh more than 50 pounds.

“I didn’t see the fish take the fly,’’ said Hawkins, who owns Bob Mitchell’s Fly Shop in Lake Elmo. “But when I felt her hit, I had a pretty good strip-set, I thought. Then, when I saw her turn sideways, I knew she was the biggest muskie I’d ever hooked.’’

Twin Cities muskie guides and fly anglers Ben Olsen and Gabe Schubert were fishing with Hawkins. The pair had been out on Mille Lacs the previous two days without a strike.

After Hawkins hooked his big fish, Olsen grabbed a landing net.

“The muskie took the fly about 25 feet from the boat,’’ Hawkins said. “Then she came straight for us, giving about six or seven giant head shakes as she did.’’

Hawkins fought the monster fish with a 12-weight fly rod he made himself, the same size rod that saltwater anglers use for tarpon, sharks and sailfish. When the muskie was alongside the boat, Olsen netted it.

“Once she was in the net, we left her in the water and were extremely cautious how we handled her,’’ Hawkins said. “Our goal was to have her out of the water only briefly. And we did. We measured her girth and length quickly and took a couple of quick photos before reviving her in the water and letting her go.’’

To qualify as a state record, the fish would have had to be killed and weighed on a state-certified scale. But killing the muskie was never an option, Hawkins said.

“That wouldn’t happen,’’ he said.

The Minnesota muskie record, taken on any bait or lure (the state has no subcategory for fly-caught fish), weighed 54 pounds, was 56 inches long and had a girth of 27¾ inches.

Hawkins’ fish was 57 inches long with a 26½-inch girth.

“I’m told that the IGFA (International Game Fish Association) has world records for fly-caught fish that are released,’’ Hawkins said. “But I have no idea. I don’t really care. It doesn’t matter to me.’’

November is one of the best months to catch a large muskie in Minnesota, and Mille Lacs, Lake Vermilion and Lake of the Woods, among others are capable of record-setters.

Hawkins said he’s been predisposed to chasing big fish since he was little.

“When I was 11 years old, I was with my dad on Flathead Lake in Montana, fishing lake trout ... and we caught a big one I could see about 30 feet through the clear water,’’ he said. “Ever since then, I’ve wanted to catch big fish.’’

Hawkins was a Montana fly-fishing guide when he met his wife, Rhea, who grew up in St. Cloud. The couple moved to Minnesota about three years ago after purchasing Bob Mitchell’s Fly Shop.

Rhea Hawkins is a graphic designer in Minneapolis.

A video of Hawkins catching the muskie is on the Facebook page of the couple’s business.