Yeah, its due to crawlers detecting through scent, the military supposedly use the same method on escape and evasion exercises, by traveling through rivers it helps throw any persuing dogs off their scent.
Thats why I always carry a stack of deoderizers with me, it makes me laugh when I see pt's wiped out in crawlers nest because of a bad pull and massive link, simply popping a deoderizer will stop all the aggressors dead in their tracks just like water, and people say deoderize is the most useless spell in the game, pfft!