Huge “sea snot” phenomenon takes over the sea in Thessaloniki Greece boosted by global heating and an overload of pollutants. A thick layer of organic matter known as marine mucilage has spread in the Thermaikos Gulf, covering the shoreline and swathes of the surface in Thessaloniki, the second-largest city of Greece.

Sea snot phenomenon is thick, slimy gray-brown sheets, known as marine mucilage, are made up of dead and living organic material, much of it phytoplankton. These microscopic algae usually help fill the ocean waters with oxygen, but when stressed they can grow out of control and produce a sticky mucus-like substance that can span many square kilometers.

Some "sea snots" are associated with the production of natural toxins, depletion of dissolved oxygen or other harmful effects, and are generally described as harmful algal blooms. The most conspicuous effects of these kinds of red tides are the associated wildlife mortalities of marine and coastal species of fish, birds, marine mammals, and other organisms.