An endangered species is a type of animal that is seriously at risk of dying out.

The contamination (making less pure) of air, water, or soil due to harmful substances, usually as a result of human activities. There are different types of pollution, for example: chemical pollution, light pollution, or noise pollution.

A fish or other marine species that is caught accidentially while fishing for something else. For example dolphin or turtle being caught in nets meant to catch only fish; or too young or too small fish caught in nets that were meant to catch only larger fish.