水甜茅（学名：Glyceria maxima）为禾本科甜茅属下的一个种。

Glyceria maxima (Hartm.) Holmb. (syn. G. aquatica (L.) Wahlenb.; G. spectabilis Mert. & W.D.J. Koch; Molinia maxima Hartm.; Poa aquatica L.), commonly known as Great Manna Grass, Reed Mannagrass, and Reed Sweet-grass, is a species of rhizomatous perennial grasses in the mannagrass genus native to Europe and Western Siberia and growing in wet areas such as riverbanks and ponds. It is highly competitive and invasive and is often considered to be a noxious weed outside its native range.