The barnacle lives in brackish and salt water. The crustacean is currently in a larval stage where it must find somewhere to settle down and build a hard limestone shell, and then boat owners must be careful.

- The hard limestone shells make the boat heavier and go slower through the water, the boat then draws more fuel. Then they can also sit in places that affect mechanics such as propellers and rudders, says Patrik Lindqvist, project manager at the Swedish Boating Union.

Reduce toxins in the water

The Swedish Boating Union has meters along the Baltic coast that show how many barnacle larvae there are in the water. In the middle of the week, high levels of barnacles were shown at Oaxen, Västerhaninge, Trollbacken, Äpplarö, Håtö and Vreta.

The purpose of the measurement is that boat owners, instead of using toxic bottom paints, should choose to wash the hull before the larvae build limestone shells on the boats.

- It is also environmentally friendly to keep the boat clean because you then draw less fuel, he says.

Has it become more common for boat owners to choose to wash instead of using toxic paints?

- Yes absolutely. Before they discussed this was to paint the easiest way, but now the awareness is much greater so then you wash more.

One of the places where you can wash your boat is in Södertälje guest harbor and more people went there than usual last weekend. See more about it in the video above.