Freshwater has almost no salt in it.
Ponds and lakes are filled with fresh water.
Rivers and streams are moving water.
A glacier is a frozen river of ice.
Plants and animals live in or near freshwater.
About three quarters of the earth's surface is covered with water.
The water biome is divided into freshwater (water with little or no salt in it) in ponds, rivers, streams and marine, or salt water (ocean biome).
Ponds and Lakes
A pond is a shallow hole where water collects. Plants generally grow around the edges of the pond, and often right across the whole pond. The temperature of the water is similar at the surface and at the bottom of the pond. The bottom is generally covered with mud. There are usually no waves. In places where winters are very cold, the whole pond can freeze solid.
Some ponds are seasonal, and only fill at certain times of the year when there is rain.
A lake is bigger than a pond, sometimes thousands of square metres. Plants can only grow along the shoreline because the water is too deep away from the edges. Some lakes are so big that there are waves.
In summer, the temperature of the water in a lake is not the same: the top part of the water gets more of the sun's heat and is warm (about 19-25ºC), the middle layer is cooler because it gets less of the sunlight (aobut 8-19ºC) , and the bottom layer, which does not get any sunlight, is quite cold (about 4-8ºC).
'Winterkill' and 'Summerkill'
In a lake, more creatures live in the warmer layer of water.
Even in the coldest places, most lakes are so big and deep that they don't freeze solid in winter, but a layer of ice can form across the surface. The ice blocks out the sunlight, and oxygen levels in the water drop, killing some plants and animals. This is called 'winterkill'.
In all freshwater areas around the world, algae (say al-gee) can be found. Algae are not plants, animals or fungi. There are different kinds of algae, and most are single-celled but some have more than one cell. As they make their food by photosynthesis, algae release oxygen into the water. Photosynthesis uses sunlight as a source of energy to combine carbon dioxide, water and salts to form chlorophyll . This means algae are most abundant in summer. When there is too much algae, the decaying algae reduce the oxygen levels in the water, and this can kill plants and animals. This is called 'summerkill'.
Rivers and Streams
Rivers and streams are moving strips of water. The water flows in a channel. The bottom of the channel is called the bed and the sides of the channel are called banks.
Rivers are large and flow into the ocean. Rivers and streams make up about 3% of the earth's total fresh water. Rivers and streams drain the earth of excess water.
Water falls from the sky (precipitation) as rain, hail, snow or sleet. Once it reaches the ground, some of the water is absorbed by trees and other plants and the rest filters down into the ground. Most water runs off the surface and eventually joins a creek or stream.
Small streams join together to form rivers. Sometimes small rivers join together to become extremely large rivers. When this happens, the small rivers are called tributaries.
A watershed is an area of land where rain water, streams and small rivers all drain into one large area of water such as a large river, lake or ocean. Because ground water also drains from a watershed, all kinds of pollution can find its way to the ocean from many kilometres away. The biggest rivers have the biggest watersheds.
Therefore, biomes with lots of consistent rain have more rivers and streams. Deserts have little rain and fewer rivers. Desert rain is short but very intense, so dry rivers and lakes suddenly become full for a short period of time.
The mouth of a river is where it meets the ocean. Rivers carry soil along as they move, and this is dropped at the mouth of the river as it enters the ocean, and gradually builds up, making new land. This is called a delta. Rivers tend to branch off in many directions through the delta, creating many islands.
Rivers that are permanently frozen are called glaciers. Glaciers are found in places such as Antarctica, the frozen continent where the South Pole is located, but glaciers are also found in countries where there are very high mountains. Even though they are frozen, glaciers are indeed rivers and do move very slowly down the mountain to the sea.
Plants and Animals
The freshwater biome is found in every continent, and the animals and plants are different in each. Members of the crocodilan family are found in freshwater wetlands in a number of countries such as Africa, Australia and parts of the USA. Crocodiles generally stay in more salty water near river mouths, but some are found in freshwater habitats. Alligators are mostly found in freshwater wetlands and rivers. Many other kinds of reptile such as snakes and lizards, and crustaceans such as yabbies, live in, on or near freshwater habitats. Frogs, turtles and tortoises are generally found in and near rivers, streams, ponds and wetlands. Freshwater fish, such as the Murray cod, and the larvae of many insects, for example dragonflies, also live in freshwater. Birds, such as the brolga, live and feed on or near freshwater wetlands.
In Africa, hippopotamus live in and around water holes and rivers in the grasslands, and the pygmy hippopotamus lives near water in the rainforest.
In parts of eastern Australia, platypus are found in rivers and streams.