Staff in Brooklyn's Prospect Park discovered the lizard on Sunday morning. It is said to go by the moniker Godzilla.
In warm-climate states like Florida and Louisiana in the southeast of the United States, alligators are native.
The city of New York experienced highs of 9C on Sunday (48.2F).
The animal was found in bad health, "extremely sluggish, and possibly cold shocked," according to NYC Parks, the agency in charge of the city's open spaces.
The alligator's origin in the lake is unknown, but the authorities has issued a warning to locals not to release creatures into the city's parks,
which it claimed was against the law. The alligator, which is being "examined," caused no harm to anyone, according to NYC Parks.
The authority stated that non-native wildlife can "lead to the loss of native species and bad water quality" in addition to the "possible hazard" of letting animals loose in the city's parks.
Around 500 reports of animal-related incidents are handled by Urban Park Rangers across the city each year, according to NYC Parks.