Cyanobacteria and Cyanotoxins in sources of Norwegian drinking water


Report no: 2021: 13

Published: 21.06.2021

Key message:

In Norwegian lakes, there are several cyanobacteria that can produce cyanotoxins (toxins), which can pose challenges for producing safe drinking water.

Thus concludes the Norwegian Scientific Committee for Food and Environment (VKM) in a knowledge summary prepared for the Norwegian Food Safety Authority.

In the report, VKM provides an overview of the occurrence of various cyanobacteria and cyanotoxins and assessed the challenges they may pose for safe drinking-water production.


There are several thousand species of cyanobacteria in soil, fresh water and salt water, but only a few produce cyanotoxins.

It is an important principle that all cyanobacteria should be considered potentially toxic until analyses prove differently.

Of the cyanobacteria identified in freshwaters in Norway, Aphanizomenon, Dolichospermum, Microcystis, Planktothrix, Woronichinia and Tychonema can produce toxins.

Three groups of cyanotoxins have been detected in Norway. Microcystins are investigated most and have been detected most often.

All three groups can cause serious health effects. Among other things, they can affect the nervous system and liver in humans and animals, and at worst lead to death. In Norway there have been some cases of poisoning of animals on pastures and in nature, but there are no known incidents of acute poisonings of humans after consuming drinking water.

Raw water sources in Norway are examined sporadically when cyanobacteria are suspected present in a water source. The Regulations on drinking water do not require monitoring, but some raw water sources with known occurrence of cyanobacteria have been monitored systematically over many years.

Warmer climate - a challenge

Cyanobacteria growth is influenced, among other things, by temperature, light, nutrients, and carbon dioxide.

"Therefore, climate change with higher temperatures and more precipitation can lead to more frequent growth of cyanobacteria," says Ingunn Samdal, Chair of the project.

“Warmer climates result in warmer water, a longer growing season and longer ice-free periods. Climate change can also cause other species of cyanobacteria to thrive. Increased rain and more floods will pose a risk of more runoff, which in turn will result in an increased supply of nutrients to drinking water sources,” Samdal explains.

Measures to achieve clean drinking water

VKM has also summarized measures for limiting the occurrence of cyanobacteria and cyanotoxins in water sources.

The main measure is to prevent or reduce the supply of nutrients. VKM points out the importance of improvements in municipal wastewater and surface water systems, purification of emissions from industry, and measures in agriculture such as reduced fertilization, plowing and land clearance. Good planning of cities and towns to avoid runoff is also important.

"In the production of clean drinking water, it will be necessary to combine different water treatment methods to remove both cyanobacteria and cyanotoxins," Samdal points out.

VKM's conclusions are uncertain due to lack of data from Norwegian raw water sources.

-In order to assess whether the presence of cyanobacteria and cyanotoxins in raw water sources is a challenge for the production of safe drinking water, we need a better database, says Samdal.

This knowledge summary has been approved by VKM's Panel on Contaminants.


Ingunn Anita Samdal

Member of VKM's Panel on Contaminants. Dr.Scient.

M: 91 17 91 38

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