I was messing around with spawners again and saw that tadpoles were being spawned, even when there was no water around, resulting in them dying by lack of water. I tried this with other aquatic mobs that require water to live, like dolphins, and it doesn't seem to happen as they will spawn normally in water and at their appropriate spawn height.

Command to reproduce

/setblock ~ ~ ~ minecraft:spawner{SpawnData:{entity:{id:"minecraft:tadpole"}}}