Fish that are close to waterlogged blocks but are still outside of their boundaries don't suffocate even though they should. Confirmed with Cod, don't know about other kinds of fish.

How to replicate:

1. Place a stair block.
2. Place water in the stair making it waterlogged.
3. Use a spawn egg or fish in a bucket to spawn one or more fish near the stair.
4. Watch as the fish don't fall in the water and remain outside of it.
5. The fish will not suffocate despite being outside of the block.