N.Y.C. Admin. Code § 10-123: § 10-123 Bathing in public.

It shall be unlawful for any person to swim or bathe in any of the waters within the jurisdiction of the city, except in public or private bathing houses, unless covered with a bathing suit so as to prevent any indecent exposure of the person; and it shall be unlawful for any person to dress or undress in any place exposed to view. Any person who shall violate or refuse to comply with the provisions of this section shall, upon conviction thereof, be punished by a fine of not more than ten dollars or by imprisonment not exceeding ten days or by both such fine and imprisonment.