The temperature was 18 degrees Monday evening when Nolan Sprengeler and a couple of buddies broke ice at a public access on Mille Lacs to drop Sprengeler's 621 Ranger into the big lake.

Sprengeler, along with Kevin Kray of Ostego and Zack Skoglund of Zimmerman, had already checked three other launches before deciding their only bet was to break the ice for about 100 yards to get the fiberglass boat into open water.

"We had thought about fishing after Thanksgiving, but looking at the temperatures we figured we better go Monday night," Sprengeler said. "We weren't sure we could get on the lake after that."

An avid muskie fisherman, Sprengeler tries to fish Mille Lacs in fall until the lake freezes, or at least until it is impenetrable by boat. The goal is to catch a muskie in the 50-pound class, a memorable fish that would make freezing fingers and iced-up rod guides worth the effort.

Sprengeler, 27, of Plymouth, exceeded that goal about 9 p.m. Monday when he hooked a muskie that tipped the scales at 55 pounds, 14 ounces.

The female fish — and it almost certainly was a female — topped the state's previous muskie high-water mark of 54 pounds, set in 1957 on Lake Winnibigoshish.

Sprengeler hooked the fish on the lake's west end while casting a large soft-plastic bait to a rock reef.

"I wanted to release it,'' Sprengeler said. "We tried for an hour to revive her. But she bit on the far end of a cast and she was hooked extremely deep in the gill plate. We had all the right equipment to get her released. We had cut the hooks with a bolt cutter. But she wasn't going to make it.''

Sprengeler said a friend's memory rode in his boat with him Monday night.

" 'Muggs' was his name. He was my neighbor and longtime friend who passed away shortly before we went fishing,'' Sprengeler said. "I believe he played a major role in helping me catch that muskie.''

Minnesota Department of Natural Resources fisheries chief Brad Parsons said Sprengeler did the right thing.

"What an incredible fish,'' Parsons said. "I think this is a very positive thing for Minnesota fisheries, and I hope [Sprengeler] won't be vilified for keeping it.''

The fish had a clipped pectoral fin, indicating that DNR fisheries personnel had handled it either in 1999 or 2008, possibly placing its age at 22 years. Muskies at this latitude, Parsons said, can in some instances live to 30 years.

"But we just don't know,'' he said.

Mille Lacs muskies feed on ciscoes in the fall to prepare for winter. The lake's biggest muskies are vulnerable then, but only to anglers willing to brave frigid weather while casting repeatedly, trip after trip — thousands upon thousands of times, in some cases — with no response.

In 2015, also in November, Robert Hawkins, owner of Bob Mitchell's Fly Shop in the Twin Cities, caught a 57-inch muskie on a fly rod. That fish is a state fly-fishing catch-and-release record.

The catch-and-release Minnesota muskie record, meanwhile, for anglers employing conventional bait-casting gear is 57 1/4 inches, caught in Lake Vermilion this summer.

Sprengeler's big fish took a circuitous route to a weigh scale.

"Once we knew the fish wasn't going to make it, we put it in my live well and packed it with ice,'' he said. "The next day, we called around, but couldn't find a certified scale that weighed more than 30 pounds and also included ounces. Finally, we ended up at a UPS store in Golden Valley.''

The fish was officially measured at 57 34 inches with a 29-inch girth.

Will Sprengeler's fish-of-a-lifetime, which is now awaiting a taxidermist's handiwork, reign atop Minnesota muskies for 64 years, like the Winnibigoshish record it toppled?

Unlikely, because in 2019, DNR staff electrofishing on Mille Lacs surfaced a muskie measuring 61 12 inches — a fish that would best not only all Minnesota muskie records but also the world muskie record of 60 14 inches caught in Lake Court Oreilles near Hayward, Wis., in 1949.