Over fifteen years (1985–1999) waterfowl were counted during one day in January on 33 permanent routes with a total length of c. 310 km along the banks of all rivers and ponds throughout the city. 23 species (apart from gulls) were recorded. The number of species varied from 3 to 10 in different years and increased significantly during the study period. Mallard Anas platyrhynchos was the most numerous species (98–99% of individuals). The proportion of male Mallards varied from year to year within the range 54–63%. The number of Mallards gradually increased from c. 17 300 in the winter of 1984–1985 to c. 28 000 in the winter of 1989-90 but then declined to c. 7500 in the winter of 1997–1998. These changes appear to depend on both air temperatures during the winter and the prosperity of the city's inhabitants, who feed ducks with bread and scraps of food. It is highly probable that the change in the socio-economic situation has been the main cause of the decline in waterfowl observed during the 1990s.