Perennial water body usually refers to mainly liquid fresh water, as opposed to sea and glaciers or other ice. Most frequently the term refers to running water (

lotic River ecosystems are flowing waters that drain the landscape, and include the biotic (living) interactions amongst plants, animals and micro-organisms, as well as abiotic (nonliving) physical and chemical interactions of its many parts.Angelier ...

ecosystems) as in

perennial stream A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long, large stream ...

s and large

river A river is a natural stream of fresh water that flows on land or inside Subterranean river, caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of ...

s, but the distinction between perennial and non-perennial water is of equal importance in

lentic A lake ecosystem or lacustrine ecosystem includes biotic (living) plants, animals and micro-organisms, as well as abiotic (non-living) physical and chemical interactions. Lake ecosystems are a prime example of lentic ecosystems (''lentic'' ref ...

aquatic ecosystem An aquatic ecosystem is an ecosystem found in and around a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environ ...

s, those that are associated with relatively still terrestrial waters such as

lake A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...

s and

pond A pond is a small, still, land-based body of water formed by pooling inside a depression (geology), depression, either naturally or artificiality, artificially. A pond is smaller than a lake and there are no official criteria distinguishing ...

s. Simplistically a perennial water body is one that keeps full or flowing throughout the year for all or most years, but in practice there are degrees and kinds of distinction. The definition is not precise, because most water bodies vary in fullness according to the season, and according to the heaviness of precipitation and other factors during any given year. Also, the water level in many such water bodies as do not actually dry out, may nonetheless drop so drastically that their surface area is greatly reduced. They even may be split into several separate water bodies with dry land between, either arid or covered with vegetation. The internal ecology of such water may differ drastically between periods of drought and deep water. In some cases the seasonal cycle is ecologically important, whereas in other examples exceptional water levels are too rare to be taken routinely into account. There also may be effectively permanent changes; increasingly frequently even large rivers have lost their perennial status under the burden of the human demand for fresh water for purposes of agriculture, industry or the needs of the populations of large cities. The

Colorado River The Colorado River () is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and in northern Mexico. The river, the List of longest rivers of the United States (by main stem), 5th longest in the United St ...

for instance has run dry for extended periods in most years since 1960 without reaching the sea. Intermittent or ephemeral streams are those that run dry repeatedly, either seasonally or soon after rain stops. Some definitions of perennial water bodies specifically include those that only are perennial except in years of severe or unusual drought. Perennial standing (lentic) water is usually called a

or a

, but there are several local or dialect English words for such features. Examples include

mere Mere may refer to: Places * Mere, Belgium, a village in East Flanders * Mere, Cheshire, England * Mere, Wiltshire, England People * Mere Broughton (1938–2016), New Zealand Māori language activist and unionist * Mere Smith, American television ...

, tarn,

loch ''Loch'' ( ) is a word meaning "lake" or "inlet, sea inlet" in Scottish Gaelic, Scottish and Irish Gaelic, subsequently borrowed into English. In Irish contexts, it often appears in the anglicized form "lough". A small loch is sometimes calle ...

fen A fen is a type of peat-accumulating wetland fed by mineral-rich ground or surface water. It is one of the main types of wetland along with marshes, swamps, and bogs. Bogs and fens, both peat-forming ecosystems, are also known as mires ...

. Each has a special meaning, though modern usage tends to be loose.

Vlei A vlei (; ) is a shallow minor lake, mostly of a seasonal or intermittent lake, intermittent nature. It even might refer to seasonal ponds or marshy patches where frogs and similar marsh dwellers breed. Commonly, vleis vary in their extent, or e ...

is a foreign example that may or may not mean a perennial body of water, but more often than not refers to a seasonal pond.

References

Bodies of water {{hydrology-stub