CONCORD, N.H. - A Massachusetts teenager who spent three nights alone on Mount Washington in April after he sprained an ankle and veered off marked trails has been fined more than $25,000 for the cost of his rescue.

Scott Mason had been praised for utilizing his Eagle Scout skills, sleeping in the crevice of a boulder and jump-starting fires with hand sanitizer gel. But authorities say he was not prepared for the conditions he encountered and should not have set out on such an ambitious hike.

“Yes, he’d been out there in July when you could step across the brooks,’’ said Fish and Game Major Tim Acerno. “And people have been out there in winter in hard-packed snow. But with these spring conditions, it was soft snow; it was deep snow.’’

Acerno said he believes that Mason’s fine is the largest ever sought under a nine-year-old New Hampshire law that allows lost hikers and climbers to be charged for rescue costs. Mason’s rescue was particularly expensive because the helicopters the state typically used were unavailable, and a helicopter from Maine had to be brought in, Acerno said.

Mason’s family said they would not comment on the bill, which was mailed July 10. Mason has until Aug. 9 to pay the bill; he could also take the state to court to contest the fine.

Mason, 17, of Halifax, had planned to spend one day hiking 17 miles in the New Hampshire mountains but ended up lost after he hurt his ankle and decided to take a shortcut. The shortcut led him into rising water and deep snow caused by unseasonably warm weather.

Mason was negligent in continuing up the mountain with an injury and veering off the marked path, Acerno said. Negligence, he said, is based on judging what a reasonable person would do in the same situation.

“When I twist my ankle, I turn around and come down,’’ Acerno said. “He kept going up.’’

In New Hampshire, for the year ending June 30, there were 131 missions that cost $175,320, Acerno said. He did not know how many resulted in fines.

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