About 1978 a small colony of cormorants was noted in the Dordtse Biesbosch. In 1990, however, only 160 nests were noted. It was concluded that this was not a viable colony. This count was carried out on the request of the Dutch ‘Rijkswaterstaat’, the powerful Dutch State Water Authority. The conclusion was that the colony was less healthy than elsewhere in The Netherlands. (Per nest, on average, raised only 0.5 surviving birds whilst an average of 3.4 surviving birds per nest was noted in other areas) It was not clear as to why this was so, lack of food caused by pollution seemed to be the major culprit. Since 1995 there has been a general improvement of water quality and the cormorant colony has clearly increased in numbers. The year 2000 saw the colony increase in numbers to 352. Since this time there has been a further gradual reduction in the numbers of breeding pairs. The most probable cause has been the disappearance of suitable nesting trees. In 2013 there were only 146 breeding pairs noted.