Welcome to the California Water Quality Monitoring Council Welcome to the California Environmental Protection Agency
Governor's Website
My Water Quality: Pollution Sources and Health Risks

Safe to Eat Fish & Shellfish
Pollution Sources & Health Risks

Preparing fish

What are the Sources of Fish and Shellfish Contamination?

Most California fish consumption advisories involve four primary contaminants: mercury, PCBs, DDTs, and dieldrin. These and other chemical contaminants persist for long periods in the environment. Persistent organic chemicals, such as PCBs, DDT, and dieldrin accumulate in fatty tissues. Mercury, on the other hand, accumulates primarily in muscle tissue. Levels of all of these contaminants increase as they are transferred up the food chain. For example, concentrations of mercury in top predators (such as largemouth bass) may be a million times higher than concentrations in water.

These pollutants originate from a number of past and present municipal, industrial, and agricultural sources, such as mercury and gold mining, pesticide use around homes and in agriculture, leaking electrical transformers, and chemical manufacturing.

The history of gold mining in California's Sierra Nevada Motherlode began with the Gold Rush of 1848/49 and is well known. Mercury, mined mainly in the Coast Range, was used to amalgamate the gold. Between 1848 and 1981, 88% of the mercury mined in the United States came from the northern Coast Range of California. The map on the right shows the historic extent of gold, silver, and mercury mining in California. Mercury contamination from mining activities persists to this day and contributes to the mercury that accumulates in fish. Other sources of mercury include emissions from the burning of fossil fuels and oil refining, the deposition of those atmospheric emissions, municipal and industrial wastewater discharges, and urban runoff.


What are the Risks of Eating Contaminated Fish and Shellfish?

The amounts of chemicals found in sport fish in California are not known to cause immediate sickness. But chemicals can collect in the body over time and they may eventually affect your health or that of your children. Some of the adverse health effects that might occur from long-term exposure to high levels of toxic chemicals in fish include increased risk of cancer, damage to the developing nervous system in the fetus and in young children, and damage to the reproductive system.

  Information for Fish Consumers:


How Can I Reduce My Risks from Eating Contaminated Fish and Shellfish?

Fish and shellfish are an important part of a healthful diet. There are things you can do to help lower your chances of taking in harmful chemicals when you eat fish. You can protect your health while benefiting from this nutritious source of food.


Seafood Sustainability

The seafood choices that you make can help the sustainability of our ocean resources.