The ecosystem is the ecological framework within which flora and fauna exist and thrive. The aquatic ecosystem covers the components of the hydrological system: lakes, rivers, streams and wetlands, but is defined also by floodplains, catchments and estuaries which constitute complex and interrelated hydrological systems. Each of these components function in a larger ecological landscape influenced by the other components of the hydrological cycle including adjacent terrestrial systems. Management of the ecosystem involves ensuring that flora and fauna exist in harmony with their environment. Changes to the ecosystem occurring naturally are usually slow to make an impact. Man-made changes can upset the balance of the ecosystem and cause it to be unstable. Damage may be irreversible, long-lasting and cause further negative effects. Ecosystem management principles require that changes made to the aquatic environment are environmentally sensitive and will not have an adverse impact on other components or the entire ecosystem.

Further information: Protection of water resources and aquatic ecosystems, UN Economic Commission for Europe, 1993.