Only 3% of all water in the world is freshwater. 99% of that is either frozen or in aquifers. Freshwater ecosystems are rivers, lakes, ponds, streams and marshes. Lakes contain three layers: littoral zone, limnetic zone, and profundal zone. The closest zone is the littoral zone, closest to the shore. It is inhabited by fish, frogs, small crustaceans and such. The next zone is the limnetic zone, which is the open water where the photosynthesis occurs. They are inhabited mostly by plankton and nekton. The last zone is the profundal zone where bottom dwellers lie, contains decomposers and no light reaches in this zone. Streams and rivers differ from ponds and lakes because they have faster currents. The animals survive more on energy from the land than from plants and such.

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Freshwater Puffer (Tetraodon mbu)

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Freshwater Stingray (Potamotrygon humerosa)

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Freshwater Barracuda (Ctenolucius hujeta)


Brackish water is water that has more salinity than freshwater but not as much as salt water. Common ecosystems with brackish water are estuaries and mangroves. Estuaries often have brackish water because it's where freshwater rivers meet the saltwater sea. Fishing is often done in estuaries because many fish live in both river and sea, therefore

it makes a great fishing ground. Mangroves are important because they are breeding grounds for many fish and act as a natural defense against hurricanes and tsunamis. There are also a few lakes and seas that are brackish water due to freshwater from land mixing with saltwater such as the Baltic sea.


Salt water covers 97% of water in the world. All oceans and most seas are salt water. Most of aquatic life occurs in oceans. 72 percent of the world is cover by oceans. Salt water cannot be used as viable source of hydration because the salt dehydrates the body. Millions of different species of fish, mammals, plants, and decomposers live in salt water, especially the oceans. It is easier to float in salt water because of the higher density from the salt. Lot of seafood comes from salt water biomes. Valleys, mountains, and volcanoes also exist in oceans.