To see how dry ice reacts in a pond frozen over with a thin layer of ice, “King of Random” Grant Thompson dumped a full bucket of it into his small fish pond. The dry ice easily broke through the pond’s icy layer and trapped carbon dioxide gas bubbles underneath.
After discovering the Styro-Slicer doesn’t cut Dry Ice very well, I decided to throw 2 bags of the stuff into our frozen fish pond instead. The result was satisfying. Note: No fish were in the pond.