The Massachusetts Department of Health (DPH) issues Fish Consumption Advisories based on industrial contaminants in fish tissue, such as Polychlorinated Biphenyls (PCBs) and heavy metals like mercury. These pollutants are harmful to humans and wildlife when ingested and often make their way into human diets when people eat fish that has lived in contaminated rivers. The DPH has published advisories for maximum fish consumption for all three rivers based on mercury contamination. Advisories may specify the fish species and which human populations should limit or avoid eating the fish.
Advisory levels for the three rivers range from P1 to P6. The whole Assabet, the Upper Sudbury upstream of Ashland, and the Lower Concord have the P1 advisory based on statewide atmospheric deposition of mercury. The P1 level means children under 12 years of age, pregnant women, women of childbearing age who may become pregnant, and nursing mothers should not eat any fish species from the water body. The Upper Sudbury (starting at the Nyanza Superfund site in Ashland) and Lower Sudbury have a P6 advisory that recommends that no one at all should consume any fish from the water body. The advisory for the Upper Concord downstream to the Faulkner Dam in North Billerica is P1 for all species, P2 (no one should eat any of the affected fish species) for largemouth bass, and P4 (the general public who are not children under 12 years of age, pregnant women, women of childbearing age who may become pregnant, or nursing mothers, should limit consumption of all other fish to two meals per month).