This is a plugin that adds scuba sound effects (breathing & occasional bubbles) when under water. It doesn't use any lua or sacrifice any stock marathon sounds, so it should be compatible with pretty much anything.

note1: stay underwater for at least 45 seconds to get the full effect.

note2: I got the samples from pond5.com, I didn't record them myself.

note3: there are two known bugs: if you use the 'underwater' sfx in your map as an ambient sound you'll get the breathing along with it, and the bubbles sound happens in vacuum levels. I'll release another version if I can figure out how to get around these.

made the breathing sound a hair louder