Fishing

I took a boat out on the lake, and tossed in a fishing line. I caught a fish. A blue gill was twisting away on the line. I unhooked its mouth. 

The fish said "I'll give you a $1000 if you let me go." 

I asked how the fish would get that kind of money. 

The fish said, "Never mind, just row your boat to that big rock over there. Underwater is a metal container. Inside is $1000." 

I set the fish down next to me on the boat, and rowed over to the rock. I reached down into the water and found the box. I took the box out, opened it up, and found the money. 

I thanked the fish. 

The fish said, "I knew there was a good reason for me to set that money aside."