What are blue green algae

Blue green algae are bacteria in surface water which look like seaweed. They convert carbon dioxide to oxygen by using sunlight. Their cells are simpler than those of other (green) algae and they usually have a green colour. Some species are however red to brown. The scientific name for blue green algae is cyanobacteria.

Blue green algae can cause major problems for recreational users of a water body. They produce toxins that can make humans and animals sick. 

Growth period

During periods of warm weather, blue green algae can grow quickly. Overnight the algae consume a lot of oxygen in the water, leaving little for other animals like fish.

The optimal temperatures for blue green algal growth is between 20 and 30 degrees Celcius and therefore the development of blue green algae or scum layers often take place from July on. The highest concentrations of blue green algae usually occur in August and September.

Scum layers

Some species form a layer of scum. This is an increased concentration of cells at the surface. A scum can accumulate at the banks of lakes, on beaches and in marinas.