When Dolphins choose to leap out of the water, they do not consider what is infront of them. Thus occasionally if a Dolphin is too close to the shore, they will end up leaping onto the land and panicking on the beach. Along with that, since the dolphins don't determine where land NOR where water is, they usually fail to return to the water, eventually suffocating on the surface.
(This report is very similar to the following issue below, but the issue there was about the dolphins trying to reach another body of water between blocks and leaping too far. This report is of dolphins just leaping in a random direction and accidentally hitting land. Please do not mark this as a duplicate of