The record low levels of the Danube this summer have caused a drastic drop in bird populations along the Bulgarian and Romanian stretch of the river, environmental group WWF said Tuesday. A week-long WWF bird watching expedition at the end of June counted 3,145 pairs of nesting birds -- herons, cormorants, spoonbils and ibises -- 500 fewer pairs than last year, it said in a statement. The number of birds was also lower compared to another WWF census in 2006. When the river levels are low, water does not penetrate the wetland areas and birds have nowhere to nest as their feeding grounds run dry, Ivan Hristov, freshwater coordinator at the WWF Danube-Carpathian Programme, explained. \"If this is accidental it will not be a problem in the long run. However, if the level of the river is going down long-term, then we are facing serious consequences,\" he said. Ten years ago, WWF initiated the establishment of the so-called Lower Danube Green Corridor, where the governments of Bulgaria, Romania, Moldova and Ukraine engaged to preserve a total of 935,000 hectares of wetland area and restore another 224,000 hectares of former bird habitats that had run dry.