Yes, EELGRASSES is a Scrabble word!

Letter values in Scrabble US: E 1, E 1, L 1, G 2, R 1, A 1, S 1, S 1, E 1, S 1.

Is it a valid word?

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

submerged marine plant with very long narrow leaves found in abundance along North Atlantic coasts
submerged aquatic plant with ribbonlike leaves; Old World and Australia

Also: grass wrack, sea wrack, zostera marina, tape grass, wild celery, vallisneria spiralis.