Fishes and other aquatic resources are captured from a great variety of freshwater ecosystems, most of which are natural.

Natural aquatic ecosystems include lakes, swamps and floodplains, collectively called standing waters, and rivers and streams, collectively called running waters.

Distribution of natural waters

The distribution pattern of natural freshwaters among the continents is uneven which has important implications for aquatic production, inland fisheries and aquaculture. For example, the greatest occurrence of standing waters is in the relatively unproductive northern areas of the Northern Hemisphere. In contrast, the distribution of running waters in the form of perennial rivers is more homogeneous, with the exceptions of the great deserts of North and Southwest Africa, the Arabian Peninsula and Australia.

The status and trends of aquatic ecosystems, both natural and modified, are closely linked to the condition of adjacent terrestrial ecosystems. Therefore, it is essential to view each inland aquatic ecosystem in terms of the watershed, or basin, in which it occurs. This applies particularly to the multiple use aspects of inland systems that require integrated watershed development, integrated watershed management and a framework within which to assess the environmental impacts of land-based activities on inland aquatic ecosystems.