Environmental health investigations branch

Mercury in Fish

Fish and shellfish are an important part of a nutritious and healthy diet. However, some fish contain mercury and other chemicals that may be harmful to your health. This page can help you and your family make healthy choices about which and how much fish to eat, especially if you fish in California's water bodies.

Online Courses (continuing medical education credits available)

These free, one-hour online courses are for physicians, health professionals, and others interested in mercury and fish.

California Fish Advisories

Fish advisories provide information to make healthy choices on eating fish caught in California.
California Fish Advisories - Office of Environmental Health Hazard Assessment (OEHHA)
Fish and Mercury page - OEHHA

Northern California Fish Brochures

Safety Tips for Eating Fish for Families ... English (PDF) ... Spanish (PDF) ... Russian (PDF)

Sacramento-San Joaquin Delta Program

Delta Mercury Exposure Reduction Program Materials - Sacramento-San Joaquin Delta Conservancy web page for Central and South Delta; Sacramento River and Northern Delta; and San Joaquin River regions.

Frequently Asked Questions

Where does mercury come from?

Mercury is a naturally occurring element found in many places. A large source of mercury in California is from gold and mercury mines during the Gold Rush. Liquid mercury was used in mining and washed into soil, rivers and streams. Mercury can be released into the air from coal burning power plants and volcanoes. When released this way, mercury; can travel long distances and fall back onto the ground or into water in rain or snow.

How does mercury that is in the water get into fish?

Mercury from volcanoes, coal burning power plants, and mines gets into the water. In the water, the mercury is turned into a form that can be absorbed by fish. Small fish become contaminated with mercury, which are then eaten by larger fish. The largest fish have more mercury because they eat lots of smaller fish and they tend to live longer, so they build up more mercury in their bodies over time. Mercury attaches to the protein in the muscle, or fillet, of fish, and cannot be removed by cooking or cleaning the fish.

How can mercury harm the health of children?

When exposed to high amounts of mercury, children and babies may have problems learning, paying attention, remembering things, walking and talking. A developing fetus (or unborn baby), babies, children and teenagers are more vulnerable to the harms of mercury than adults because their brains are still developing, and it takes smaller amounts of mercury to cause health problems. During pregnancy, mercury can pass from a mother to the fetus. In smaller amounts, it can also pass into breast milk. Older children are also vulnerable to mercury because their brains are still developing.

How can mercury harm the health of adults?

The brain and nervous system are most affected by mercury. Adults exposed to high amounts of mercury may have problems with headaches, numbness and tingling, loss of balance, difficultly walking, shaking, difficulty hearing, and changes in vision, among other problems. It takes about 70 days for the amount of mercury in your body to decrease by half, once you stop eating high-mercury fish. A person can reduce the amount of mercury in their body substantially by limiting consumption of fish for three months or more.

What is a fish advisory?

In order to protect families from the harms of mercury from fish, it is important to check local fish advisory when eating fish caught in California. A fish advisory provides information in order to make healthy choices on eating fish caught in the state, and will help identify fish to eat that are low in mercury and other chemicals.

Where can I find California fish advisories?

Fish advisories can be found on this California fish advisory page: https://oehha.ca.gov/fish/advisories

The California EPA, Office of Environmental Health Hazard Assessment or OEHHA has a page on fish and mercury: https://oehha.ca.gov/fish/

What is the best way to limit exposure to mercury in fish?

Fish is a healthy source of protein. The best way to limit one's exposure to mercury is to choose fish
with lower levels or to eat smaller portions of mercury-containing fish. Consult advisories to determine which fish are best to eat for pregnant women and children.

Resources

Fish
2017 Advice about Eating Fish and Shellfish - U.S. Environmental Protection Agency/U.S. Food & Drug Administration joint advice
Office of Environmental Health Hazard Assessment - OEHHA web page
Biological monitoring for mercury within a community with soil and fish contamination - Journal article abstract