The Plants & Animals That Live in Rivers

The highly diverse ecosystems of rivers span all the climate zones and exist in every part of the world, providing homes to an equally diverse group of plants and animals. The unifying feature of most river ecosystems is the presence of flowing, fresh water that is high in nutrients from erosion and rainfall runoff.

Northern River Otters

The northern river otter, or Lontra canadensis, is a ubiquitous river mammal found in most of the United States and Canada, excepting southern California, New Mexico, Texas, and desert regions of Nevada and Colorado. River otters also live in the deltas of the Rio Grande and Colorado River in Mexico. Otters thrive in freshwater or marine habitats, including rivers, river deltas, estuaries and swamps. The animals are semiaquatic and have streamlined bodies covered in thick, oily fur for insulation under water. They have an average body length of 3 to 4 feet and weight can range from 4.99 to 13.6 Kilogram. Male otters are typically larger than females.


Perennial watercress, or Nasturtium officinale, thrives in wet, swampy areas, such as found near shallow water and riverbanks. The young stems of this plant are commonly used as a garnish or in salads. The plant produces smooth, compound leaves and stems; the leaves grow partially submerged. Watercress grows wild in flooded areas and rivers all across the United States and grows commercially in unshaded pools of shallow, flowing water. This plant prefers moderately cool environments.

Eurasian water milfoil

Eurasian water milfoil is also known as spike water milfoil and the scientific name Myriophyllum spicatum. This plant is tolerant of many different water conditions and is considered an invasive weed in many places due to the large infestations it can form. This perennial plant that grows submerged in water with its roots planted in soil at the bottom. The stems of the plant range in colour from reddish-brown to whitish-pink and can grow to lengths of 6 to 9 feet. The soft, feather-like leaves are 2 inches long with deep divisions. Water milfoil displays small flowers that are reddish in colour and held above the water level on flower spikes.


Piranhas are the most infamous river inhabitants in the world, thanks to their aggressive feeding habits. These small fish swim in schools called shoals and possess unusually long teeth. They range in size from 6 to 18 inches and in colour from grey or blue to black. Most species live in warm, fresh, flowing water, such as is found in the Amazon River system. To reinforce their reputation as vicious carnivores, these fish eat almost anything, from fruit and berries to other piranhas. Caimans, snakes, turtles and birds are the fish's natural predators.

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