N.Y. Town Law § 300
Each owner of two adjoining tracts of land, except when they otherwise agree, shall make and maintain a just and equitable portion of the division fence between such lands, unless both of said adjoining owners shall agree to let their said lands lie open, along the division line, to the use of all animals which may be lawfully upon the lands of either; provided, however, that the owner of an adjoining tract of land who does not keep such animals thereon within five years of the date of the erection or repair of a division fence shall not be obligated or liable for erecting, maintaining or repairing such a division fence under this article. Unless otherwise agreed, an adjoining owner who erects or repairs a division fence shall be entitled to recover from the owner of the other adjoining tract, twenty percent of the proportionate cost thereof otherwise ascribable to such other owner for each year or part thereof in which the other adjoining tract is regularly used for keeping animals occurring within five years of the date of such erection or repair. When the adjoining lands shall border upon any of the navigable lakes, streams or rivers of the state, the owners of the lands shall make and maintain the division fence between them down to the line of low water mark, in such lakes, streams or rivers except those lands which overflow annually so as to be so submerged with water that no permanent fence can be kept thereon, and known as low flat lands; and when adjoining lands shall be bounded by a line between the banks of streams of water not navigable, and the owners or occupants thereof cannot agree upon the manner in which the division fence between them shall be maintained, the fence viewers of the town shall direct upon which bank of the stream, and where the division fence shall be located, and the portion to be kept and maintained by each adjoining owner.
N.Y. Town Law § 300