Algae bloom in Tjörnin pond

This scum develops when certain blue-green algae or bacteria reproduce too quickly and form a bloom that begins as murky sediment but becomes a film floating on the water's surface. People are asked not to feed bread to the ducks during this time, since adding more organic matter to Tjörnin pond would make the situation worse.

This phenomenon is called eutrophication and happens when nutrient levels become excessive. This is a common condition in still waters during summer months, though it's not ideal. Conditions are especially likely to develop when water temperatures rise during warm, sunny days and when water circulation is poor due to slow flow.

The scum is highly visible and can give off a strong smell. While it's not considered hazardous, people are advised to avoid touching it unnecessarily.