Why is the Algae in my local river or lake?

Cathal Walsh
Environmental Blogger
Thursday, 25th April 2019
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Swan swimming on a lake going toward some algae

Algae are primitive microscopic organisms found in nearly every river and lake in the world. They consume nitrogen and phosphorous nutrients in the water and along with photosynthesising, this allows them to grow and reproduce. Algae serve a purpose because they feed small animals called zooplankton which then goes on to serve as food for fish. Algae can also produce some of the oxygen found in lakes. For these reasons algae are good and provide a service to every river and lake they may be found it.  They are essential to both the health of the lake and the health of the fish and other animals in the lake.

Algae grow in a lake or river where there is adequate sunlight, enough nutrients and the right temperatures for their particular needs. The amount and type of algae in a river or lake can vary with the changing of the seasons. The amount of algae in water tends to be at is highest in early summer due to the rising temperatures, more sunlight during the day and an abundancy of nutrients due to winter rains.  Because of these reasons however the level of algae will start to decline in mid-summer usually and in late summer it will be characterised by blue-green algae and less of it.

Despite being essential to a healthy river or lake, algae can also be detrimental to a water source in some instances. Most of these however are caused by the overgrowth of algae. When algae grow too thick they can coat docks and pipes, they can even grow so thick that they inhibit plant growth in the water source.  They can also create odour and taste problems and cause skin conditions such as swimmers itch.  Some algae may even produce toxins which can be deadly to pets and livestock, also dangerous to human health.

The main types of algae around are blue-green algae and filamentous green algae. Blue green algae are the most prolific due to their shape. Due to their shape they are more difficult for zooplankton to eat and are also responsible for many of the toxic algae blooms you may see in rivers and lakes.

If you want to control the level of algae blooms in a river or lake it is best to understand first that the primary cause of such algae is an excess of nutrients in the water.  Therefore the best way to battle them is to control the amount of nutrients going into the lake.  Doing things like using no-phosphorous fertilisers, maintaining septic tanks regularly and controlling run off so that it doesn’t go into the river or lake is key.  Planting a buffer of native plants next to the shore of a river or lake so that the nutrients are used up by the plants instead is also an excellent way of controlling algae levels.

The best form of maintenance is monitoring however, if you are unsure what is causing algae in a certain water source near you be sure to get the water tested to find out. Once you know be sure to keep up the testing regularly so that you can monitor the behaviour of the river or lake correctly.

Follow the link to purchase a River water quality test : https://www.h2olabcheck.com/product/river-water-quality-test

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