Continuous overpopulation around the Marmara sea is maybe the main reason - and noone seems to do anything about it except remote-ization due to covid19.
The article blames over-industrialization and under-investment into water treatment.
Instead of a large planned wastewater treatment plant, the powers that be decided to inject wastewater at 50m depth. They had hoped that the bulk of the wastewater will be pulled into Black Sea and not be their problem.
But this plan backfired, and phytoplankton bloomed beyond the ability of other organisms to eat it. As a result, less oxygen is available in the water, fishing has collapsed, mussels turned poisonous and can't be harvested or farmed any more.
Instead of a large planned wastewater treatment plant, the powers that be decided to inject wastewater at 50m depth. They had hoped that the bulk of the wastewater will be pulled into Black Sea and not be their problem.
But this plan backfired, and phytoplankton bloomed beyond the ability of other organisms to eat it. As a result, less oxygen is available in the water, fishing has collapsed, mussels turned poisonous and can't be harvested or farmed any more.
Penny-wise, pound-foolish :(