Based on census conducted in 1998, 2000 and 2007 to Anas flavirostris, Oxyura jamaicensis and Fulica sp. (Coots) in the el Otun Lake (Colombian Central Andes), the trends of population size of these species were described. It was determined that the populations of O. jamaicensis and Coots were reduced between 1998 and 2007 in a 63 and 54% respectively, and that the variations in the Lake level during 2000 were correlated with the changes in the abundance of A. flavirostris. The results suggest that these species change in abundance both intra and inter annually and that they could be related with environmental variations. On the other hand, some disturbances (the fire occurred in 2006) could have affected the state of these populations reducing them even more. It is a priority to continue with the population monitoring of these species because of their reduced population size which makes them more vulnerable to stochastic environmental and demographic factors.