Startide Rising — David Brin

The Terran exploration vessel Streaker has crashed on the uncharted water world of Kithrup, bearing one of the most important discoveries in galactic history. Above, in space, armadas of alien races clash in a titanic struggle to claim her. Below, a handful of her human and dolphin crew battles armed rebellion and a hostile planet to safeguard her secret--the fate of the Progenitors, the fabled First Race who seeded wisdom throughout the stars.