Umibōzu

is the boss of the sea. It was used by Amachi to terrorize the Land of the Sea in the Land of the Sea arc. Umibozu itself is nothing more than water that has been gathered and held together by chakra, making it virtually indestructible unless it is completely evaporated. It was defeated by Naruto Uzumaki throwing an explosive tag attached to a kunai into Gamabunta's oil.