Sayyiduna Jabir bin Abdullah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) was asked about sea water, and he (peace and blessings be upon him) said: "Its water is pure and its dead animals are lawful."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1195