Big Water

From Land Before Time Wiki

"Big Water" is a Land Before Time term for the ocean. It is the place where Mo and Elsie live. The water is salty. The island where the gang encountered Chomper in the 5th movie is surrounded by this. It is also near the big water while looking for Littlefoot and his friends that the Great Valley adults found a spot with plenty of fresh water and green food for the herd to stay till the great valley regrew and they were able to return.

They return again in the 9th movie when they help Mo to return to the big water, though it seems to be not the same place as part of the 5th movie took place.