GENEVA, Nov 1 (Reuters) - More than a third of freshwater fish species in Europe face extinction due to overfishing, pollution and dams which have caused rivers to dry up, a scientific study said on Thursday.

The continent's 522 freshwater fish species are under a much higher level of threat than birds or mammals, according to the study "Handbook of European Freshwater Fishes", published in collaboration with the World Conservation Union (IUCN).

"With 200 fish species in Europe facing a high risk of going extinct, we must act now to avoid a tragedy," said William Darwall, senior programme officer at IUCN's species programme.

Twelve species are already extinct following a century of development which has had a devastating impact, the study said.

The European eel, which reproduces only once on average at around 20 years, is critically endangered, it said. The number of juvenile eels reaching European coasts has dropped dramatically in the past three decades.

The jarabugo, found in southwestern Spain and Portugal, is also endangered as its population has declined by more than 50 percent in the past 10 years.

"Large dams built for irrigation, flood control and power generation have had major impacts upon species in large rivers and have led to local extinction of numerous migratory species", the Swiss-based IUCN said.

This has led to some rivers drying up in the summer months, a phenomenon which was "becoming more acute with the impacts of climatic changes", it said.

Areas subject to the highest levels of threat include the lower reaches of the rivers Danube, Dniestr, Dniepr, Volga and Ural, the Balkan peninsula and southwestern Spain, it added.

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