Biomagnification, also known as biological magnification or bioamplification, is the process by which certain substances, such as pesticides or heavy metals, increase in concentration in the tissues of organisms at successively higher levels in a food chain. This process often occurs in aquatic environments, where substances work their way into lakes, rivers, and oceans, and then move up the food chain in progressively greater concentrations as they are incorporated into the diet of aquatic organisms such as zooplankton, which in turn are eaten by fish, which then may be eaten by bigger fish, large birds, animals, or humans.

There are several related terms that are important to understand when discussing biomagnification:

• Bioaccumulation: This occurs within a trophic level and is the increase in the concentration of a substance in certain tissues of organisms bodies due to absorption from food and the environment.

• Bioconcentration: This occurs when uptake from the water is greater than excretion and is defined as occurring within an organism.

• Biodilution: This is the opposite of biomagnification and occurs when a pollutant gets smaller in concentration as it progresses up a food web. It is a process that occurs to all trophic levels in an aquatic environment.

Biomagnification can have severe effects on the health of organisms, causing disease, genetic mutations, birth defects, reproductive difficulties, behavioral changes, and death in many marine organisms. The severity of the damage varies greatly between species, but animals near the top of the food chain are often most affected due to the process of biomagnification.