Around 1,500 inhabitants of the Tigris valley in southeastern Turkey will request asylum in Switzerland, Germany and Austria if the planned Ilisu dam goes ahead.
Non-governmental organisation the Berne Declaration said on Tuesday that people's homes would be flooded.
The three European states last year granted export-risk guarantees to contractors taking part in the project, which include Swiss-Swedish electro-engineering giant ABB.
One hundred inhabitants of Hasankeyf, a historical town that would be covered by the dam's waters, travelled to the Turkish capital Ankara to hand over letters from their region's population to the Swiss, German and Austrian embassies.
In a statement, the Berne Declaration said that any asylum requests would be a direct consequence of Switzerland's implication in the project.
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