Last year, the fish were displaced from their usual freshwater habitats after flooding forced them into the sea, which experts believe killed them.

Their bodies poured into the port of the central city of Volos this week.

The floating carcasses created a silvery blanket across the port and caused a stench that alarmed residents.

Authorities now face a race against time to collect and remove the tonnes of dead fish before the smell reaches nearby restaurants and hotels.

"It spans kilometres. It's not just along the coast, but also in the centre of the Pagasetic Gulf," city council member Stelios Limnios said, referring to the area offshore of Volos where the coast is lined with holiday homes.

Trawlers dragged nets through the water to collect the fish and dumped them in the back of trucks.

Over 24 hours this week, more than 40 tonnes of fish were collected, authorities said, with the operation still ongoing.

Volos mayor Achilleas Beos said the smell was unbearable and blamed the government for not dealing with the fish before they reached the city, during a press conference on Wednesday.

Dimosthenis Bakoyiannis, 33, who owns a beach restaurant six miles (10km) from Volos, says his turnover dropped 80% this summer as fewer tourists wanted to visit.

"Closing the barrier now doesn't help. Now it's too late, the tourist season is over."

Mayor Beos also referred to the decision not to place a net at the mouth of the river leading into Volos, to catch the fish.

"They didn't do the obvious, to put a protective net," he said, referring to the government.

Mayor Beos also warned the rotting fish could create an environmental disaster for other species in the area.

The problem was caused by historic floods last year that inundated the Thessaly plane, further north, experts said.

When the fish, used to freshwater, met the sea, the saltwater likely killed them.

Local prosecutors have ordered an investigation.

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The disaster is just the latest impact of extreme weather in Greece, that scientists link to climate change.

The country has faced severe wildfires this year, and erratic rainfall has caused flooding too.