Residents of Izmir Bay, located along Türkiye’s western coast, are once again confronted with the foul odor that occasionally plagues the area, as environmental experts warn that pollution is causing recurring ecological problems in the bay.
Dr. Levent Yurga, a faculty member at Ege University’s Faculty of Fisheries, identified bacteria that decompose both dead planktonic organisms and dead vertebrate and invertebrate animals as the main source of the persistent odor.
“The proliferation of cyanobacteria, diatoms and dinoflagellates has caused mass fish deaths. Even cartilaginous fish, typically the most resilient species, were affected at the beginning of 2025,” Yurga said. He emphasized that the odor will continue unless pollution is significantly reduced.
The unpleasant smell had first spread across Izmir Bay last year following mass fish deaths. While no mass fish deaths have been recorded this year, the odor has resurfaced as rising temperatures accelerate the decomposition of organic matter in the water.
According to Yurga, Izmir Bay began experiencing severe odor problems in the 1990s due to unchecked industrialization and the direct discharge of domestic and industrial wastewater into the sea. Early attempts at mitigation, such as covering streambeds with concrete under the so-called “rehabilitation” projects, failed to address the root causes of the problem.
In the 2000s, the Izmir Metropolitan Municipality launched the Great Canal Project, which directs domestic and industrial waste to biological treatment facilities. The removal of Ragıp Paşa Lagoon, which previously blocked the bay’s natural currents, also allowed the bay to self-clean through water circulation.
These measures led to visible improvements in water quality, allowing marine species, such as seagrasses, sea hares, seahorses and tube worms, to gradually spread from the outer bay into the middle and inner areas. Biodiversity continued to improve steadily until the early 2020s.
Yurga explained that pollution has begun to rise again as wastewater treatment capacities have not kept pace with the growing population. “Alongside vertebrate and invertebrate species carried in ships’ ballast water, some dinoflagellate species, a group of phytoplankton, entered the bay. Excess nutrients from pollution allowed them to overgrow. Between 2023 and 2024, these organisms covered almost the entire bay, reducing oxygen levels and triggering mass fish deaths,” he said. Misguided attempts to control these blooms disturbed the ecological balance rather than restoring it.
Yurga stressed that removing sea lettuce and using short-term chemical or physical methods to kill overgrown species is both ineffective and harmful. “Sea lettuce and other marine plants are crucial for oxygenating the water and providing habitat for marine life. The only long-term solution is to halt pollution at its source, particularly in rivers like the old branches of the Gediz River, where industrial waste continues to flow,” he said.
The expert also emphasized that blaming global seawater temperature rises alone is an oversimplification. “Overfishing in Izmir Bay has weakened natural ecological controls. If fish populations were stable, they would consume jellyfish and sea urchin larvae that feed on bacterial plankton, preventing excessive jellyfish proliferation. By overfishing and allowing pollution to continue, we are destroying the bay’s ecosystem,” he added.
Yurga concluded with a warning to policymakers and residents: “If we want to leave a clean and balanced bay for future generations, we must focus on long-term solutions and stop treating only the symptoms. Addressing pollution at its source is the only way to restore Izmir Bay’s natural ecological balance.”
