Fishing from ponds.

My starting evac shelter was close to a small pond that had fish in it. I early on created some fish traps from gallon jugs and have been successfully fishing it. It is now summer day 66 and when I activated my reloaded fish trap as I had been doing regularly I received the message "You doubt you'll have much luck catching fish here."

What would be the explanation for why I received the message? Did I fish out all the fish? Do the ponds dry up? I looked at the water and it says "shallow water" though I have no idea if it was shallow water when I was successfully fishing as I never looked at the water tiles.