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 Assabet has the P1 advisory based on statewide atmospheric deposition of mercury. Under P1, 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 Lower Sudbury (starting in Ashland) has a P6 advisory that recommends that no one at all should consume any fish from the water body.