ÇORLU, Turkey — Pollution readings on the Ergene River fell sharply after 2,800 workers walked out of seven dyeing and finishing plants in the Thrace region, researchers said on Thursday. Chemical oxygen demand, a measure of substances that consume oxygen in water, dropped by 76% at three monitoring stations downstream in five days.
Dissolved oxygen rose from 1.2 milligrams per litre to 5.4, while electrical conductivity fell 41%, according to the Ergene Basin Observatory, a research group that has tracked the river since 2012. The strike began on 19 September over shift schedules and overtime pay. Its environmental effect has startled scientists who have spent years measuring the river’s decline.
A sudden natural experiment
“We have never seen the river change this quickly without a major change in flow,” said François Lemaitre, a hydrologist with the observatory. Rain gauges showed no significant rainfall during the sampling period, and an upstream station recorded little change, making a sudden dilution from weather unlikely, he said.
The seven plants’ combined wastewater discharge fell by 79% during the walkout, according to flow meters checked by the researchers. The facilities continued treating wastewater already in their systems, but took in far less water from production. Researchers collected samples daily and sent them to a laboratory in Edirne for testing.
“People have argued for years about what the factories contribute. For five days, the river gave us an answer,” said Clarice Rico, a representative for the striking workers. She said the union had not called the walkout over pollution and did not coordinate with the researchers.
The Ergene, which passes through one of Turkey’s main manufacturing corridors before joining the Meriç River, has faced complaints about discoloured water and persistent odours for years. The latest results do not show that the river is clean: oxygen levels remain uneven, and the measurements cover only a short stretch and a brief period.
What happens when plants reopen
Evangelista Negri, an environmental chemist advising the observatory, said the readings were a powerful clue but not a complete explanation. The river also receives runoff from farms, towns and other industries; longer tests are needed to separate those sources and identify which pollutants fell most during the stoppage.
The observatory plans to continue sampling twice a day if the strike ends, and has asked the regional water directorate to preserve access to the outfall meters. The plants’ owners have not announced a restart date. Union negotiators said talks were scheduled for Friday, with staffing levels and overtime rules still unresolved.
Scientists hope the brief pause will help them target the next phase of testing, including checks for dyes and salts that can remain in river sediment after water readings improve. But the immediate concern is more basic: if production returns at its previous pace, researchers expect the river’s chemistry to move back in the opposite direction within days.
