In the lower left corner of the base screen you see "Ecodamage: 0" in green if everything is right.

(If things are heating up you can see "Ecodamage: 12" for example. The number is the chance that a tile inside the city radius will turn into fungus. (Expressed in percent.)
I generally feel that I can live with a chance in the single digits. But if it gets to 10+ and I can't do anything about it (in a war so I need the production, and no eco damage reducers available) then I station an empath rover in the base.