Middle English, from Anglo-French or Latin; Anglo-French, from Latin incontinent-, incontinens, from in- + continent-, continens continent: not continent: as a (1): lacking self-restraint (2): not being under control
Applied via once-common colloquialism to a particular portion of said hoofed creature, it could describe a very different sort of "flood".
Either that, or you're talking about a really big llama.
My aeronuatics prof at Caltech once joked that an incontinent engine was one in which your reactants combine over the wrong continent. /ba-dum-bum