Pollution in California

Pollution in California relates to the degree of pollution in the air, water, and land of the U.S. state of California. Pollution is defined as the addition of any substance (solid, liquid, or gas) or any form of energy (such as heat, sound, or radioactivity) to the environment at a faster rate than it can be dispersed, diluted, decomposed, recycled, or stored in some harmless form. The combination of three main factors is the cause of notable unhealthy levels of air pollution in California: the activities of over 39 million people, a mountainous terrain that traps pollution, and a warm climate that helps form ozone and other pollutants. Eight of the ten cities in the US with the highest year-round concentration of particulate matter between 2013 and 2015 were in California, and seven out of the ten cities in the US with the worst ozone pollution were also in California. Studies show that pollutants prevalent in California are linked to several health issues, including asthma, lung cancer, birth complications, and premature death. In 2016, Bakersfield, California recorded the highest level of airborne pollutants of any city in the United States.

The Federal Clean Water Act defines water pollution as "dredge spoil, solid waste, incinerator residue, sewage, garbage, sewage sludge, munitions, chemical wastes, biological materials, heat, wrecked or discarded equipment, rock, sand, cellar dirt, and industrial, municipal, and agricultural waste discharged into water." In 2011, an Environmental Protection Agency (EPA) study showed that water quality standards were not met on 1.6 million acres of California's 3 million acres of lakes, bays, wetlands, and estuaries. The Porter-Cologne Water Quality Control Act governs the water quality regulation in California.

There is also an effect on agricultural sector of extreme weather, sea level rise, and wildfires. After the 2024 election there was a change of government interaction with global climate policies. Now in 2025 president Donald Trump withdrew the United States from the Paris Agreement. With Clean Air Act (CAA) there is a limit of certain containment pollutions in efforts to help clean the air. This limits many industrial and chemical plants in the amount of releasing chemical pollutants.