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Water stagnation occurs when water stops flowing. Stagnant water can be a major environmental hazard.

[edit] Dangers

Malaria and dengue are among the main dangers of stagnant water, which can become a breeding ground for the mosquitoes that transmit these diseases.

Stagnant water can be dangerous for drinking because it provides a better incubator than running water for many kinds of bacteria and parasites. Often times, stagnant water is contaminated with human and animal feces, particularly in deserts or other areas of low rain.

[edit] Causes and prevention

Stagnant water may be classified into the following basic, although overlapping, types:

• Water body stagnation: stagnation in lakes, lagoons, rivers, etc.
• Surface and ground water stagnation
• Trapped water stagnation. The water may be trapped in human artifacts (discarded cans, plant pots, tires, dug-outs, roofs, etc.), as well as in natural containers, such as hollow tree trunks, leaf sheaths, etc.

To avoid ground and surface water stagnation, drainage of surface and subsoil is advised. Areas with a shallow water table are more susceptible to ground water stagnation due to the lower availability of natural soil drainage.

Excessive watering may cause ground or surface water stagnation.

[edit] Life that may thrive in stagnant water

Some plants prefer flowing water, while others, such as lotuses, prefer stagnant water.

Various anaerobic bacteria are commonly found in stagnant water. For this reason, pools of stagnant water have historically been used in processing hemp and some other fiber crops, as well as of linden bark used for making bast shoes. Several weeks of soaking makes bast fibers easily separable due to bacterial and fermentative processes known as retting.

• Denitrifying bacteria
• Purple bacteria (both sulfur and non-sulfur)
• Leptospira

[edit] Fish

• Northern snakehead fish
• Siamese fighting fish
• Pygmy gourami
• Spotted barb
• Lepisosteidae (gar)
• Walking catfish

Mosquito larvae in stagnant water

[edit] Insects

Stagnant water is the favorite breeding ground for a number of insects.

• Mosquito larvae
• Fly maggots
• Dragonfly nymphs
• Nepidae (water scorpions)

[edit] Other

• A number of species of frogs prefer stagnant water.
• Algae
• Biofilm
• Some species of turtles
  • Mata mata

[edit] See also

• Water pollution
• Residence Time Distribution