Kyle is a little old for this and never cared for jello, but want to keep this in mind for a future crafty project.
It was posted over at Three Princes Designs
It is just made of blue jello gummi fish in a clear plastic container and it looks like a finshing pond.
The instructions indicated to make the jello according to pkg and pour into a clear containter and set up to a soft consistency the pour in some gummy fish and put back in the fridge until it is set.
I also found the same concept over at Enchanted Learning
On this blog it also has the same thing except either in clear plastic cups, a large clear punch bowl for an aquarium look or freezing them into popsicles - how cool (pun intended) is that!