A large algal bloom, also referred to in Greece as the “Red Tide,” has once again turned the waters of the Thermaikos Gulf along the Thessaloniki waterfront a murky brown, raising environmental concerns in Greece’s second-largest city as warmer weather and favorable winds intensify the phenomenon.
In recent days, large sections of the city’s seafront have been covered by a thick, brownish layer of phytoplankton slime. The bloom has produced unpleasant odors and altered the appearance of one of Thessaloniki’s most recognizable public spaces, affecting areas used daily by both residents and visitors.
Brown algal bloom spreads along Thessaloniki’s seafront
Drone footage highlights the scale of the algal bloom, showing brown waters stretching along Thessaloniki’s seafront from the Concert Hall area toward the city’s historic promenade.
According to local reports, rising temperatures and southerly winds have helped drive the algae toward the shoreline. As a result, the material has accumulated along the coast, forming a continuous layer across the water’s surface in several parts of the gulf.
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Scientists point to eutrophication as cause of Thessaloniki waterfront algal bloom
Scientists attribute the phenomenon to eutrophication, a process driven by excessive concentrations of nutrients such as nitrogen and phosphorus entering the marine environment.
In the case of the Thermaikos Gulf, these nutrients can originate from urban wastewater, river runoff and agricultural fertilizers. Combined with higher sea temperatures, this leads to the creation of ideal conditions for the rapid growth of phytoplankton. This, in turn, can result in dense algal blooms that alter the color of the water and generate strong odors as the organic material begins to decompose.
Thermaikos Gulf remains vulnerable
Environmental experts have repeatedly warned that the Thermaikos Gulf is particularly vulnerable to such episodes due to long-standing pressures linked to urban development, agricultural activity, and climate-related factors.
Similar outbreaks have periodically been recorded in recent years, especially during warmer months, making algal blooms a recurring problem for Thessaloniki and the wider coastal area.
Cleanup operations underway as algal bloom spreads across Thessaloniki
The latest bloom follows earlier signs of eutrophication that have been reported in the Thermaikos Gulf since the beginning of the year.
Authorities have continued cleanup and monitoring efforts, including operations by the anti-pollution vessel Alkippi. The vessel has been deployed to assist in the collection of floating organic material and limit the impact of the bloom on coastal areas.
Long-term measures needed
Experts stress that algal blooms are generally natural biological processes, but they can be intensified by human activity and environmental pressures.
Reducing the frequency and severity of such outbreaks will require long-term measures to improve water quality, limit nutrient inflows, and strengthen environmental management across the wider Axios-Thermaikos Basin.
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