This is an article about the character mentionned in The Shadow Over Innsmouth. For the one created by Henry Kuttner, see The Hydra.

Mother Hydra is a creature who, alongside her consort Father Dagon, is said to rule over the race known as the Deep Ones.

There is debate as to whether or not Mother Hydra is a lesser Great Old One or merely a grotesquely mutated Deep One - though the latter seems more likely as she doesn't seem to show much in the way of supernatural power outside her gigantic size and unnaturally long life span.