Blue-green algae

Blue-green algae are mainly found in fresh stagnant water such as ponds, but also in swimming pools. They float on the surface of the water, forming a layer that resembles oil. As the layer thickens and the algae have less space they die. This creates a greenish, smelly mush. The green mush causes less light to enter the water. The breakdown and lack of light means less oxygen enters the water and can also kill fish and other aquatic animals.

Blue-green algae produce toxins. These are harmful to humans and animals. Common symptoms are skin rashes, headaches, fever and gastrointestinal problems. Small children are more likely to be affected because they regularly ingest some water while swimming.

Water quality monitoring

The official swimming season for natural waters runs from May 1 to October 1. During this period, water quality is measured at least once a month at designated swimming locations in South Holland, including the Zoetermeerse Plas (Noord Aa). Here, samples are taken at 3 locations: at the swimming beach, the play pond and the nude beach. The monitoring is done by the Hoogheemraadschap van Rijnland by order of the Province. The water is mainly examined for pathogenic bacteria and the presence of blue-green algae or other toxic algae.

Longer-term solutions

Blue-green algae is a current problem in Zoetermeer Lake. Several experiments have been tried to get rid of the blue-green algae. The 'Ons Blauwe Goud' project is currently underway. You can read more about it at www.rijnland.net | Ons Blauwe Goud. This project is trying to ensure that no blue-green algae develop in the Zoetermeer Lake.