# How can the pH of an acidic lake be increased?

$\text{pH}$ of a substance can be increased by adding basic substances to it. The most common one would be to put limestone or quicklime into it. Those two compounds are alkaline or basic, and will therefore reacting with the acid in the lake to neutralize it and form water, which has a higher $\text{pH}$ than the acid.
I wouldn't add to much of it though, as that will raise the $\text{pH}$ of the lake too much, and it'll turn basic, and also be harmful to the organisms living there.