i would think putting the stumps in the pond would put way to many nutrients in the water from the rich topsoil from around the stump. when i dug the pond,i cleared out an area and put the stumps there , then pushed dirt over them to make a sledding hill. after cutting more trees later that i left to close to the pond , was to burn them.you need a big hoe to beat on them and flip them around though , but they will burn in time.

i only wanted to have some fun