SAN MATEO — A 15-year-old boy who was hit by a motorized boat while kayaking in the San Mateo Marina Lagoon on Sunday afternoon is in critical condition, according to police.

The boat’s driver, 48-year-old Stephan Chiari of San Mateo, was suspected of being under the influence of alcohol at the time of the crash, according to San Mateo police. Chiari was arrested on suspicion of reckless operation of a boat, operating a boat while intoxicated, and boating under the influence with injury.

Police said the 15-year-old teen was kayaking in the slough behind the 600 block of Fathom Drive, west of Mariners Island Boulevard, when he was hit by the boat just before 4 p.m. The teen, who was kayaking with another person in a separate kayak, was rushed to the nearest trauma center, police said.

Chiari remained at the scene and cooperated with the investigation, police said. Though alcohol was determined to be a factor, the full dynamics of the collision remain under investigation, police said.