Carbon Dioxide in water is slightly acidic. Seeing how nature has plenty of both this outcome is not really very surprising. I wish whatever Judge said Carbon Dioxide was a pollutant was impeached then publicly horse-wiped. He deserves no less.
Contrary to what most people believe about breathing, the reason we change how fast we breathe is to regulate the levels of carbon dioxide, and thus, the pH, in our blood. The more you exercise, the more CO2 goes into your blood, and the faster you breathe to get rid of it so that the blood pH will not decrease.
< /end completely off-topic digression >