PARIS — A 64-year-old man admitted to operating a watercraft under the influence in a Jet Ski accident on the Saco River that injured a teenager last summer.

Robert E. Morse, of 325 Intervale Cross Road in North Conway, N.H., pleaded guilty to the charge in Oxford County Superior Court on Tuesday. The plea dismissed a more serious charge of aggravated assault.

Justice Robert Clifford sentenced Morse to serve two days of a two-year sentence and two years of probation. During his probationary period, Morse must not use or possess alcohol, submit to random searches for alcohol, attend substance abuse counseling, not operate a watercraft, complete 100 hours of community service, and pay a $400 fine.

Liam Downes, who was 19 at the time of the accident in August 2009, said in a statement to the court that he was canoeing with friends on the Saco River. He said he and other canoeists became separated from other friends and worried about getting lost. Morse agreed to give him a ride on his personal watercraft to see if they could find the group farther up the river.

Downes said Morse ignored his request to slow down, and that he was thrown from the watercraft after it collided with an object in the river. Morse was uninjured, but Downes suffered a compound fracture of his right arm after landing among branches and trees in the river.

Assistant District Attorney Richard Beauchesne said Morse’s blood-alcohol level was .22 percent after the accident. The state’s legal limit is .08 percent.

Beauchesne said Morse had no criminal history other than a 1972 speeding conviction.

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