[Dahoser]

..As he prepared his dinner, he remembered that the water lilies in their native habitat in Rwanda grew in a shallow stream, and that there is much more CO2 above water than below, so he changed the depth of the water he was using in his experiment in a bid to get them more of the gas. It worked.

Ahem. The settled science says that CO₂ is bad. A telegram needs to be sent to the lily pond so this guy can be educated properly.

[Cronos]

Like most things, it is a question of quantity - and circumstances.