There is a higher potential for mercury in runoffs in land locked lakes than the ocean.
Thats actually how we keep people from taking fish out of some of the private ponds i fish. Signs up around the pond saying warning elevated levels of mercury. Works like a charm. I will never keep a bass. Even a gut hooked bass will get released. Should it die it will feed a turtle. That being said when a pond gets over run with smaller 12-14 inch bass sometimes it is necessary to thin them out.Otherwise you end up with lots of small thin slow growing bass.