It's time to review the hull of your boat and wash away the larvae that are now trapped. This is because the barnacles are now entering.

- Oystercatchers on boat bottoms make the boat run slower, consume more fuel and emit more exhaust fumes, says Peter Karlsson, operations manager for the Swedish Boating Union.

According to the Swedish Boating Union's barnacle map batmiljo.se, there are already high levels of barnacles at the measuring station in Öregrund. But it is possible to protect yourself against the small crustaceans - if you know when they get stuck.

- In the Baltic Sea, barnacles are a fairly simple organism. They hatch like larvae and usually only get stuck once a year. If you know when it happens, they are easy to wash off.

Wash

A wash can thus be done without having to use toxic primer. The easiest way is to wash the hull, take the boat ashore or go into fresher water, says Peter Karlsson. You know it's time when the barnacles are about five millimeters in size and the shell has started to harden. It is important to grab it before the shell has become too hard.

- To know when it's time, we have about 100 observers along the shores of the Baltic Sea who check, and then report to us. If we see that it is in progress, we go out with a warning.