Yes, MARSHES is a Scrabble word!

Letter values in Scrabble US: M 3, A 1, R 1, S 1, H 4, E 1, S 1.

Is it a valid word?

MARSHES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

low-lying wet land with grassy vegetation; usually is a transition zone between land and water
United States painter (1898-1954)
New Zealand writer of detective stories (1899-1982)

Also: reginald marsh, ngaio marsh.