Water birds are important indicators of ecological change in wetland ecosystems. By estimating the species richness of waterbirds, the changes in the environmental behaviour of Bangladesh may be assumed substantially. The leading idea of this paper is to estimate the number of species of water birds of Bangladesh. Many parametric models are used for the estimation of species richness now-a-days. We fit four parametric models to the data of water birds and compared them on the basis of AIC values and standard errors. Among these models, two-mixed exponential mixed Poisson model has proven to be the best fit model.