A thick, brown layer of mucus has once again spread across the Thermaic Gulf, blanketing the entire port of Thessaloniki and creating a strong stench along with disturbing visual scenes.

The phenomenon, which appears almost every year, is caused by an intense bloom of phytoplankton. This surge is linked to the inflow of nutrients such as nitrogen and phosphorus from urban wastewater and agricultural fertilizers, combined with high seasonal temperatures.

The excessive concentration of microorganisms leads to the formation of this brown, slimy layer on the surface of the Thermaic Gulf waters.