I've thought about acid rain lately. It was big, it threatened, well....everything, it was going to cause massive damage, it was caused by thoughtless and/or evil humans practicing capitalism and on and on. And, then, poof!, it was gone. Along with Alar and DDT.
Turns out that slightly acidic granite produces slightly acidic water in lakes where granite is the predominate mineral. The flora and fauna in those areas adapt to those conditions.