Surface water quality monitoring has as its main objective the characterization of water resources as well as the monitoring of its space-time evolution in order to achieve an appropriate administration. Dissolved oxygen (DO) is an important indicator for the estimation of the water quality index, and the lack of this quality variable may cause significant environmental issues. The aim of this contribution is to propose a geostatistical model that can used to characterize and assess water quality behaviour/evolution based on a rather extended data relative to the River Douro Basin (in Portugal) that consists mainly of monthly measurements of dissolved oxygen concentration in a network of water quality along this basin. The monthly data set reports to the period between March 2002 and February 2013
