Water splashing sound location c:

[Rapture]

Sounds>Water_Lurker>water_lurker_attack.snt (Some of the others have some various loud splashes to)

It still has the Lurker screeching in the background, but the splash sound is loud enough. Might be able to open it in Audacity and see if you can remove the Lurker's sound.

Edit: Theirs like 2 versions for each .snt though, some have mostly just a large splash. If you can get the sound to only play that particular one, I think that is what you will want.