Tenn. Code Ann. § 6-56-108

Any municipality of this state may make financial contributions to any watershed development authority created by special act of the general assembly, where a portion or all of the watershed development administered by such authority lies within the county wherein such municipality is situated, and such municipality is participating directly or indirectly in such development. Such contributions shall only be made when authorized by the legislative body of such municipality from the general funds of such municipality. No special tax may be levied for such contributions. The amount of such contribution shall be fixed by such legislative body and sanctioned thereby as a municipal purpose, the development of which being beneficial to such municipality.