They’ve tried this in the UK. Result: For some stupid reason CO2, which is heavier than air, tends to find a way out of the hole you put it in. More often then not, it finds its way back to the surface through aquifers.
Animals come to the pond, lake, stream, etc to take a drink, start feeling a little woozy, and then bye bye forever. Livestock deaths in the UK due to this boneheaded play were numerous.