Not sure if the layout of the Garrison is the same to everyone, but I assume it is. In the pond of your fishing zone, there is an underwater cave where you can find a chest with resources in it. The more interesting aspect of this cave however, in my mind, is that there is a chained corpse down there.
Why is it there, and who could it be? Let me hear your theories!
EDIT:
So a quick update; The chest is called "Scrap's stolen supplies" and this gnome Scrap Sparkfuse actually swims around in the water (if you haven't opened the chest yet. Since I can't see him on my main) and if you talk to him he says "Supplies? What supplies? I have no idea what you are talking about. <Scrap's eyes ddart back and forth and he nervously clears his throat.> What? I'm not trying to steal them or anything... I mean, if I knew what you were even talking about, which I don't."