Yes, NAIADES is a Scrabble word!

Letter values in Scrabble US: N 1, A 1, I 1, A 1, D 2, E 1, S 1.

Is it a valid word?

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

submerged aquatic plant having narrow leaves and small flowers; of fresh or brackish water
(Greek mythology) a nymph of lakes and springs and rivers and fountains

Also: water nymph.