A bioindicator is a species or group of organisms used to assess the health of an ecosystem or the quality of the environment. These organisms respond sensitively to changes in environmental conditions, making them valuable for monitoring pollution levels, habitat integrity, and ecosystem changes. For example, the presence of certain macroinvertebrates in water can indicate good water quality, while their absence may suggest pollution. By studying bioindicators, scientists can gauge the impacts of human activity, climate change, and other ecological pressures, aiding in environmental conservation efforts.