A river or water flow is a natural stream of water that flows continuously through a channel on the earth's surface . It has a certain flow , is rarely constant throughout the year , and flows into the sea , a lake or another river, in which case it is called a tributary . The final part of a river is its mouth . Sometimes they end up in desert areas where their waters are lost through infiltration and evaporation (see allochthonous river ).
Rivers are part of the hydrological cycle . Water generally accumulates in a stream of precipitation through a basin of runoff surface and other sources as recharging groundwater , springs and release of stored water in natural ice and snow layers
Some freshwater fish are:
Anguilla : they are born in the Sargasso Sea . The larvae migrate to the European and North African rivers, where they reach three years of age (elvers). In the rivers they will spend between 4 and 10 years, at which time they begin their reproductive migration to the place where they were born. Adults die after reproducing ;
Catfish , in Central and South America ;
Bream : lives in smooth running waters;
Caribbean or piranha , in the rivers of South America;
Cachama , in South America;
Tent ;
Escardinio : lives in calm waters and very full of vegetation;
Sturgeon , a large Eurasian fish, with whose roe caviar is made ;
Goby ;
Ródeo ;
Rutile : it adapts to muddy waters although it prefers clear ones;
Salmon : born in mountain rivers with fast-flowing waters and stony bottoms. At the age of three they migrate to the sea and return to the river to reproduce;
Shaker , gimnoto or electric eel (South America);
River trout : lives in clear and cold waters, rich in oxygen ;
Barbel .