Is mercury in fish really an issue or just leftwing conspiracy?

Mercury...: It poisonous to the human body. Mercury levels in various foods will accumulate in the body and can cause harm. I don't know about a conspiracy but everything political seems to have some other motivations.

Can be an issue: Definitely more of an issue if pregnant or small child (developing nervous system). Little fish: little mercury. Big fish eat little fish and thus accumulate it. Not an issue for farmed fish (other issues for that). Eat small fish like sardines, herring, mackeral, salmon. Chunk light tuna is made from smaller fish than albacore so less mercury than solid white generally if you are eating canned.

Politics involved: Nobody questions that methylmercury accumulates in the food chain and that high doses it's neurotoxic, especially to the unborn child. Since nobody really has a clue about how this operates at very low doses, and there's not a shred of evidence of an effect on any population outside of two incredibly polluted sites, the EPA's required "recommendation" was something folks would accept easily.