Waukegan, Ill. • Authorities don’t know who dumped a four-foot-long reptile in Lake Michigan, but they now know what kind it is.

After initially believing the animal spotted Monday swimming near Waukegan, Illinois, by a startled kayaker was a caiman, officials now say it is actually an alligator.

Either way, it had no business paddling around the suburban Chicago shoreline and Waukegan spokesman David Motley said Tuesday that animal control officers are trying to determine who abandoned the alligator, which was found with its mouth taped shut.

Motley said officials thought the animal was a caiman for much of Monday, but the head of the Wildlife Discovery Center in nearby Lake Forest later told him it was an alligator.

The two species look similar, but an alligator's snout is more rounded and only its upper teeth can be seen when its mouth is closed, whereas a caiman's upper and lower teeth can be seen, said Andrew Biddle, the head of reptiles at Wild Florida Airboats & Gator Park in Kenansville, Florida.

Motley said the gator likely would have died within a few weeks if it hadn’t been rescued and brought to an animal control officer. He said there was a similar incident in 2012 in which someone abandoned a 14-foot python on the lakefront.