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Frequently Asked Questions

In Colorado, mercury is the contaminant in fish that is most prevalent. Mercury is a naturally occurring element in the environment. Certain natural events, such as forest fires and volcanic eruptions, contribute mercury to the atmosphere. Precipitation brings this contaminant down into waterbodies. At the local, regional, and global level, human activities, such as gold mining and chemical manufacturing, power generation, and incineration, also increase the amount of mercury that is introduced into the environment.

 Mercury can accumulate in your blood stream over time and may harm the nervous system. The segments of the population that are most at risk are young children, developing fetuses and breast-fed babies because their nervous systems are still developing. By following the statewide fish consumption guidelines and site-specific guidelines, the nutritional benefits gained from eating fish should outweigh the potential exposure to the harmful effects of mercury.

Fish bioaccumulate methylmercury by absorbing it through the food they eat. The amount of methylmercury in fish depends on the diet of the fish, age of fish, and their location in the food chain. Mercury reaches higher concentrations in long-lived species and species of fish that eat other fish. Fish and shellfish are the main sources of methylmercury exposure to humans.

Smaller fish generally contain less mercury than older and larger fish. Smaller fish, such as rainbow trout, crappies, and yellow perch, usually have lower levels of mercury because they tend to feed on plants or smaller aquatic organisms.

Predatory fish , such as walleye and lake trout, can accumulate more mercury because they eat other fish.

Mercury is bonded to the proteins in the fish muscle. Therefore, there is no cleaning or cooking method that will reduce the amount of mercury in a fish.

The exposure to some contaminants other than mercury can be affected by certain cooking methods. Some contaminants are stored in fish fat. Frying tends to seal these pollutants in. However, per the EPA, if the fish is cooked such that the fat is drained away, some of the pollutants can be removed.

Most ocean or farm-raised fish that you find at the store or restaurant such as salmon, tilapia, catfish, cod, shrimp or crab contain low levels of mercury, and the Food and Drug Administration (FDA) recommend eating two meals per week of the low-level species. However, some ocean fish do contain high levels of mercury and the FDA recommends that children, pregnant women, or women planning on becoming pregnant should not consume these species: shark, swordfish, tilefish, and king mackerel. It is important to consider all sources of fish in your diet in order to make responsible choices about fish consumption.   You can find more information on this topic from the FDA.

All fifty states have some form of fish consumption advisory for elevated contaminant levels in locally caught fish. There are currently over 3,700 fish consumption advisories for mercury on either lakes or streams in the United States. Many states have also issued site-specific guidelines, similar to Colorado’s, to better inform and protect the people of their state.