Summary:
Dolphins don't go towards water one block high when they are drying. They seek water with a height of at least 2 blocks, because of this they often do not find or very poorly find water when jump out.

Steps to reproduce:

1. Make a pool 1 block high.
2. Spawn a dolphin next to it.

Observed results:
The dolphin stands still there and dies.

Expected results:
The dolphin tries to go to the closest water it can detect.