Published on: 2.12.2019

Information produced by Finnish Environment Institute

When water looks or smells weird

What should you do when a brook has weird scum on it or smells odd? Or funny-looking goop has washed onto the lake shore?

The goopy stuff on the shore often consists of dead algae, for example blue-green algae. Blue-green algae are greenish, turquoise or yellowish in colour and smell musty. Rather than swimming in such waters, you should wait until the water is clean again. The thick layer of pollen that may build up on the shore in spring and early summer, on the other hand, is harmless.

Light-coloured foam on a shore or in a brook usually is a natural phenomenon occurring when substances produced by algae and microorganisms reduce the surface tension of water. Bacterial activity may also produce an oily film which, however, does not feel greasy on your fingers.

Actual oil can be recognised by its smell, and the fact that it feels slippery, is glutinous and sticks to rocks. If you notice oil in the water or on the shore, you should call the Emergency Response Centre. A very small volume of oil can also be collected using oil absorbent peat. You should never try and disperse oil using a solvent or soap.

Urban brooks and rivers are particularly vulnerable to contamination, as many different activities are pursued in their catchments. If you see peculiar scum in a brook or its water looks or smells weird, you should call the Emergency Response Centre. Also keep an eye out for any fish kills.

Image: © Vesa Greis, Vastavalo