When swimming through water that was placed by the player the sound works, however if the water is placed in the air and the water flows down from the source block, the ambient noises and the fog, fail to appear.

I was making an aquarium and placed a bucket of water on the bottom of a floating block, the water (as it should) flowed down in a column, when swimming in the source block the ambiance and the fog was always there, but when swimming through the water that flowed from it, nothing happened. i could still swim through it, but it was behaving as if the snapshots never even happened.

If you want to try it yourself:

1. make a ceiling up in the air.
2. place water on the bottom of every one of those blocks.
3. swim through source blocks, see what happens.
4. swim through flowed blocks, see what happens.