Final Fantasy 12 Hunt... White Mousse Where are You?

I have been searching these questions for a long time and I can't seem to find mine so I feel like a real idiot. I am trying to hunt the white mousse but I cant seem to get anywhere in the garamsythe waterway. 1 door from lowtown just says "shut tight" or something like that and the other leads to the overflow and central sluice control but I cant go anywhere from there. Is there another entrance? Is there a way to unlock the other door? What the hell am I supposed to do?