Every year a large number of migratory wintering water birds, rest in the wetlands situated in the Northern provinces of Iran. The wetlands are very important ecosystems for these creatures. Due to ecological importance of water birds, the results of this study (the birds’ populations and their changes) are helpful to monitor them and are especially important to manage the wetlands. In this study, 38 wetlands consist of the Caspian coast along all the 3 provinces, 17 wetlands in Gilan, 7 in Mazandaran and 13 in Golestan have been studied. According to the results of the water bird censuses, in the mid-winters of 2000 to 2004 (5 years), which have been utilized in this study, totally a mean number of almost 1507000 water birds (115 species) have annually wintered in the wetlands. According to these censuses, the populations mainly consist of geese, swans and ducks (52%) and rails, gallinules and coots (32%). The most abundant species were common coot (mean pop. of 479835); common teal (mean pop. of 254658) and mallard (mean pop. of 133187) respectively. Mazandaran has shown the highest mean populations and the top number of species during these 5 years. The largest number of water birds was recorded in Mazandaran with the minimum species' diversity in 2004. In the same year, the highest number of species belongs to Gilan. Golestan has got the highest species' diversity. Among the wetland areas, Gomishan and Anzali wetlands have the highest score of water bird criteria (23 points).