I had a friend who died with mercury poisoning from too much fish consumption, so the issue is real.

That said, generally this problem occurs in top ocean predators, such as swordfish and tuna. They eat many smaller fish which have mercury, and store this in their fat. I believe the FDA warning applies more to them than freshwater fish, though someone can correct me if I'm mistaken.

7ac 2015 CNBG RES FHM 2016 TP FLMB 2017 NLMB GSH L 2018 TP & 70 HSB PK 2019 TP RBT 2020 TFS TP 25 HSB 250 F1,L,RBT -206 2021 TFS TP GSH L,-312 2022 GSH TP CR TFS RBT -234, 2023 BG TP TFS NLMB, -160