I was working on lowering my All Secrets PB for Water Under The Bridge, but accidentally I found a way to clip faster. Here's a video of it, try to ignore the goon shitting please. far as I can tell, I was under the water for the speed, then when I got to the caution sign, I looked up and jumped, and then I clipped.
So i suspect that the way this clip works is when you are right between the layers of the water and air it counts your speed as running which allows you to build up speed and with that you can actually use it to save time later in the water by swimming close to the surface (just be careful to to clip back into the world) i have a clip of me doing both (messed up with the jump clip but later on it works well for the speed in the water) Apologies about the singing it was for a bit