Pond Algae

If you have walked past a pond then you may have seen algae on top of the water. Some of it is microscopic but can build up into a dense covering. Certain species of algae can even move around and swim.

Pond algae are one-celled plants. You can spot it floating on the surface of ponds, and you can also see them attached to plants around the pond and on rocks.

Pond algae are very similar to seaweed that you may find on the seashore and are actually related, with many belonging to the same group. Algae can not only be found in ponds but in many areas of freshwater.

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Algae is an essential food source along with plant material such as leaves that fall into the water. The algae, as a photosynthetic plant, uses the energy from the sun to produce sugars that are eaten by animals as a source of energy. Although not all algae are eaten by animals, some fall t the bottom of the pond indirectly becoming part of the food web. Bacteria on the pond floor along with some animals will then eat the debris.


Diatoms are a major group of algae that are microscopic. They are either made up of a group of cells and a cell wall made of silica or single cells with a silica wall.

The cell walls form together to make a variety of shapes including star shapes, boat shapes, and zig-zag shapes. When they die, the skeletons of diatoms fall to the bottom of the pond. When these fossilize they can be used in a variety of ways. The deposits, known as fullers earth can be mined and used in different ingredients in paints and toothpaste.


Along with the diatoms on freshwater ponds you can often find another tiny green alga called desmids. Whereas the diatoms can be found in saltwater, desmids are algae only found in freshwater. Desmids also only appear in green as they only contain chlorophyll, a green pigment.

The microscopic cells are divided into halves horizontally, with some having a spiky appearance while others are smooth.

Swimming Algae

Some algae, such as Chlamydomonas can actually swim. They are propelled by two flagella which allows it to swim around. This is another green algae with chlorophyll which helps it in photosynthesis.

By swimming around the algae can multiply quickly by using cell division, a pain for pond owners as the pond can turn green within just a few days.

Green algae are often banded together in colonies. Some species may only have a few cells in each colony while others have thousands. These join to make one individual about the size of a pinhead.


While some algae join together in colonies to form a larger individual, others have long mucous covered filaments. The filaments either attach to the bottom of the pond or float on top. Unfortunately, if this algae covers the entire pond then it can starve the pond of oxygen, effectively killing any other pond and animal life, including fish.

As there are shorter days with less daylight in winter, spring is the best time to see algae on ponds. The intensity of the light in spring can cause the algae to grow very quickly and the water can turn green and cloudy.

Blue-Green Algae

Not all algae contain only chlorophyll with the most primitive algae being bluish-green. Some blue-green algae are the most primitive organisms to live today. These types of algae can be either colonial or filament.

As with other algae, the cells are held together not only by the cell walls but also by a jelly substance surrounding them.

These can be found on top of freshwater as well as attached to the bottom, and can sometimes be seen as a slim on rocks.


If you have ever been by a pond that smells like rotten eggs then you may have wondered why this smell exists. Unfortunately, this is because the pond is in very bad condition because it has been choked by hydrogen sulfide gas. If the pond has been choked by the algae then this creates an oxygen-deficient condition. Hydrogen sulfide is poisonous and the pond may take a long time to recover.

Bryan Harding

Bryan has spent his whole life around animals. While loving all animals, Bryan is especially fond of mammals and has studied and worked with them around the world. Not only does Bryan share his knowledge and experience with our readers, but he also serves as owner, editor, and publisher of North American Mammals.

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