[He does stop, realizing just then how his throat feels dry and he was holding his breath so much that it leaves him in an almost gasp of air. He's not sure what hits him first, the ripples in the water not settling entirely this time, or how--]
Shiro.
[--Or how the water seems to darken like a large shadow from below, almost blending in, almost something that could have been missed if not for Keith can see now that it's coming closer. His eyes widen, struck with the full brunt force of the realization and a full blown panic in his voice.]
We need to get the hell out of--
[It's too late. Almost like it zero'd in on Keith when his eyes locked onto it, the creature swims impossibly fast at him for its size, attacks right as Keith was trying to stand, jaws digging into the side of his leg to straight up pull him into the water.]