In some cases it is permitted:
http://www.maine.gov/ifw/atv-snowmobile/atv/laws-rules.html26. Prohibited equipment. A person may not operate an ATV that is equipped with a snorkel kit or other equipment designed to allow the ATV to be used in deep water except with the permission of the owner of the land on which the ATV is operated or as provided in section 13159.
§13159 – Racing meets.
Notwithstanding section 13155 and section 13157-A, subsection 16, paragraph A, subsection 17, and subsection 25 ATVs used exclusively for scheduled racing meets and operated solely on predefined race courses are exempt from the provisions of this chapter concerning registration, mufflers, snorkel kits, and lights during the time of operation at these meets and at all prerace practices at the location of the meets.