Mercury in Maine Freshwater Fish: How to Read the State Advisories

Buy a Maine fishing license and the lawbook that comes with it is mostly what you’d expect. Season dates. Length limits. Water-by-water rules running for pages. Then you reach the appendix, where page A-4 of the 2026 edition is a health advisory about eating what you catch, printed word for word.

State law puts it there. Under 22 MRSA section 1696-I the Bureau of Health must assess regularly whether health threats exist for people eating freshwater and anadromous fish caught in state waters by noncommercial anglers, and Inland Fisheries and Wildlife is responsible for “incorporating the verbatim health advisory in the abstract of fish and wildlife laws.” Which is how a public health document ends up between the bass rules and the ice fishing dates.

What the Advisory Actually Says

Maine CDC’s statewide mercury guidance says two very different things to two groups, and the split is the whole point.

For one group the answer is zero. “Pregnant and nursing women, women who may get pregnant, and children under age 8 DO NOT EAT any freshwater fish from Maine’s inland waters,” with one exception for brook trout and landlocked salmon at one meal per month. Everyone else, “all other adults and children older than 8,” gets two freshwater fish meals per month, with brook trout and landlocked salmon allowed once a week.

Read closely, the Maine Family Fish Guide is really sorting fish into three tiers. Atlantic mackerel and sea-run smelt carry no limit for anyone, pregnant women and young children included, because they’re low in mercury and high in omega-3 oils. Freshwater smelt, landlocked salmon and brook trout sit in the middle. Everything else lands in the strictest tier: pike and pickerel, largemouth and smallmouth bass, white perch, lake and brown trout, striped bass and bluefish.

Maine also defines the unit. “A fish meal for those age 8 and over is about 4 ounces of fish, the size of a deck of cards.” Two of those a month is less fish than most people picture.

Why It Covers Every Pond in the State

The advisory isn’t a list of bad lakes. It applies to inland waters generally, because of how the metal arrives. Maine CDC puts it plainly: “Mercury in the air settles into the waters. It then builds up in fish.” Older fish carry more than younger ones, and fish that eat other fish, pickerel and bass among them, carry the most.

Air deposition doesn’t respect a shoreline, so the rule turns on species and size rather than on which pond you launched from. NHDES sketches the regional picture: coal-burning power plants account for about 42% of manmade mercury emissions in EPA’s 2014 National Emissions Inventory, and mercury landing in New Hampshire is “carried here primarily from coal-fired utilities and municipal and medical waste incinerators in the Northeast and Midwest,” hundreds of miles on the wind. Deposition rates there, “as in the entire Northeast, are higher than in other areas of the country,” with concentrations running higher in tea-colored, relatively acidic waters. Our guide to environmental health in Maine and New Hampshire covers the rest.

There’s a second reason the wording is blunt. You can’t fix mercury in the kitchen. Cleaning and cooking “will not reduce mercury in fish tissue,” Maine CDC says. “Mercury is in the fish muscle and cannot be removed by trimming or cooking.” The opposite of PCBs, dioxins and DDT, which collect in fatty tissue and can be reduced by trimming the fat away and cooking so it drips off.

The Two Numbers Behind the Split

Maine sets two mercury action levels for the same fish. The developmental fish tissue action level is 0.2 ppm, derived from a reference dose of 1.0 x 10-4 mg/kg-day. The adult level, based on paraesthesia, is 0.65 ppm, from a reference dose of 3.0 x 10-4. More than three times higher. Same fish, same water, two answers, because the endpoint being protected differs.

The 0.2 ppm figure is still the operative one. Maine DEP’s 2023-2024 toxics report calls it the more protective level CDC uses for non-commercially caught finfish, and notes it “assumes an 8 oz. meal size is consumed weekly,” while the guidance handed to the public defines a meal as about four ounces. Both appear in Maine documents, each in its own context. And an action level is a planning threshold for deciding when to issue advice, not a line where harm begins on one side and stops on the other.

Sixty Miles South, the Numbers Change

Cross the Piscataqua and the same species come with looser advice. New Hampshire’s high-risk group is pregnant and nursing women, women who may become pregnant, and children through age six, where Maine’s cutoff is 8. For rainbow and brown trout, NHDES allows the high-risk group one meal a week and everyone else six. For all other freshwater fish, brook trout included, it’s one meal a month and four. Bass, pickerel, white perch and yellow perch are further limited to fish 12 inches or less. A meal there is 4 ounces for children six and under, 8 ounces for everyone older.

From 1992 to 2016 NHDES analyzed muscle tissue from 4,100 fish, 26 species, 227 waterbodies. The average came in at 0.33 mg Hg/kg, under the 0.70 benchmark the state uses, with walleye and lake trout pushing against it at upper 95% confidence limits of 0.86 and 0.68.

Cleaner air didn’t settle it either. NHDES estimates the state’s own atmospheric mercury emissions fell 99%, from 1,109 pounds a year in 1997 to 11 in 2016, against a roughly 80% national drop since 1990. The fish only partly followed. Yellow perch declined significantly, 0.40 to 0.24 mg Hg/kg between 1995 and 2016, while largemouth bass showed no significant change from 1994 to 2015. Two states, two sets of numbers, and no published comparison of how each one got to its own.

The Mercury Rule Doubles as Maine’s PFAS Backstop

Here’s a wrinkle most anglers never hear. Maine CDC’s fish tissue action level for PFOS is 3.5 ng/g, lowered in 2022 from 34.1 ng/g for sensitive populations and 79.0 for everyone else. A sharp tightening. But because the mercury advisory already restricts most species so heavily, DEP notes that it “provides protection for up to 7.5 ng/g of PFOS in species such as largemouth and smallmouth bass, black crappie, togue, and white perch,” so no additional advisory gets considered for them below that level.

A rule written for one metal is carrying part of the load for another contaminant entirely. Maine CDC says the same about waters with no known PFAS sources: preliminary sampling came in below levels that would require advice more restrictive than the existing mercury advisory, and those fish “are considered safe for consumption, provided that consumers are following the existing consumption guidance.” PFAS reaches the region through more than fish, which the regional environmental health guide takes up.

Federal Advice Points the Other Direction

If Maine’s page reads as restrictive, joint FDA and EPA advice reads as encouragement. People who are pregnant or breastfeeding are told to eat 8 to 12 ounces a week of a variety of lower-mercury seafood, 2 to 3 servings from the Best Choices list, a serving being 4 ounces. For fish caught by family or friends, check local advisories, and where there isn’t one, “eat only one serving and no other fish that week.”

The two aren’t in conflict. Maine’s rule governs inland sport fish that concentrate mercury, while the federal advice is built around lower-mercury commercial seafood. Maine’s own top tier makes the point from the other end, putting mackerel and sea-run smelt at no limit for anyone. For readers who end up in the supplement aisle instead, our breakdown of what to look for on a fish oil label covers that ground.

The federal push has weight behind it. In the ALSPAC cohort of 11,875 pregnant women, maternal seafood intake below 340 g a week was associated with higher risk of a child landing in the lowest quartile for verbal IQ (for no seafood consumption, odds ratio 1.48, 95% CI 1.16 to 1.90, trend p=0.004), plus worse outcomes for prosocial behaviour, fine motor skills, communication and social development. The authors concluded that “risks from the loss of nutrients were greater than the risks of harm from exposure to trace contaminants in 340 g seafood eaten weekly.”

Which doesn’t make methylmercury benign. EPA calls it “a powerful neurotoxin” and says exposure in the womb “can adversely affect unborn infants’ growing brains and nervous systems,” with possible effects on memory, attention, language, fine motor and visual spatial skills, while noting that CDC data show most people carry blood mercury below levels associated with possible health effects. At the exposures most of us live with, the science is less settled than either side of the argument sounds. A synthesis in Environmental Health Perspectives led from Dartmouth found evidence that “raises the possibility” of effects on fetal growth in susceptible subgroups and on infant growth in the first two years, no clear pattern for cardiovascular risk, and immunologic results that have “been inconsistent.”

Reading Page A-4 Without Overreading It

The advisory is a statewide floor for sport fish, sorted by species and by who’s doing the eating. Not a verdict on your pond, and not commentary on the salmon at the grocery store. New Hampshire’s averages describe New Hampshire fish, and a meal limit is a risk management decision, not a measurement of what any one fillet holds. The page is short on purpose. Worth the two minutes it takes to work out which half is addressed to you.

Sources

• Maine CDC. Fish and Seafood, Safe Eating Guidelines for Mercury: maine.gov/dhhs/mecdc
• Maine CDC. The Maine Family Fish Guide (reprinted August 2021), p. 11: maine.gov/dhhs/mecdc (PDF)
• Maine Bureau of Health. Fish Tissue Action Levels, derivation document: maine.gov/dhhs/mecdc (PDF)
• Maine DEP. 2023-2024 Surface Water Ambient Toxics (SWAT) Report, pp. 40 and 56: maine.gov/dep (PDF)
• Maine CDC. PFOS in Recreationally Caught Freshwater Fish: Questions and Answers, updated August 22, 2024: maine.gov/dhhs/mecdc (PDF)
• Maine Legislature. 22 MRSA section 1696-I, the advisory as printed in Maine IFW’s 2026 Open Water and Ice Fishing Laws: legislature.maine.gov
• NHDES. New Hampshire Fish Consumption Guidelines, ARD-EHP-25 (2021): des.nh.gov (PDF)
• NHDES. Status and Trends of Mercury in Freshwater Fish Tissue for New Hampshire, 1992-2016: des.nh.gov (PDF)
• NHDES. Mercury: Sources, Transport, Deposition and Impacts, ARD-28 (2019): des.nh.gov (PDF)
• US FDA. Advice about Eating Fish, joint FDA and EPA advice: fda.gov
• US EPA. Health Effects of Exposures to Mercury: epa.gov/mercury
• Hibbeln JR et al. Maternal seafood consumption in pregnancy and neurodevelopmental outcomes in childhood (ALSPAC study). The Lancet 2007;369(9561):578-85: pubmed.ncbi.nlm.nih.gov
• Karagas MR et al. Evidence on the human health effects of low-level methylmercury exposure. Environmental Health Perspectives 2012;120(6):799-806: pubmed.ncbi.nlm.nih.gov

This article is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare provider before making any health decisions.