 Downstream from the confluence of its tributaries, the Trebižat and Bregava rivers, the valley spreads into an alluvial fan covering 20,000 hectares.The upper valley, the 7,411 hectares in Bosnia and Herzegovina, is called Hutovo Blato.Neretva Delta has been recognised as a Ramsar site since 1992, and Hutovo Blato since 2001.