Published on: 2.12.2019

Information produced by Finnish Environment Institute

Is the water safe for swimming?

How can you tell if water is safe to swim in? What kinds of problems can affect bathing water?

Potential problems in bathing water include poor hygienic quality and abundance of blue-green algae, both of which can harm your health.

Hygienic quality means checking for the presence of faeces and faecal bacteria in the water, as bathing water contaminated by faeces can cause gastroenteritis. Municipal health authorities monitor the hygienic quality of bathing areas regularly, and the results are posted on their notice boards. If you have a holiday home by a lake or the sea, you must take special care to prevent toilet waste or sewage from leaking into bathing water.

Blue-green algae are harmful because some of them are toxic, and there is no way of telling which are toxic and which are not just by looking at them. This is why you should always presume that water containing blue-green algae may be toxic. Children, in particular, should be protected from blue-green algae as they may swallow water and be poisoned by it, and the same goes for livestock and pets.

Because the toxins can also be inhaled, water containing blue-green algae should never be used in the sauna, to wash yourself or even to water plants.

The blue-green algae situation may vary from day to day. In public bathing areas, lifeguards monitor the amount of blue-green algae in the water and warn swimmers if necessary.

Image: © Riitta Weijola, Vastavalo