The paper assesses the usefulness of various methods for calculating the loads of pollutants washed out of an agricultural catchment. The data used in the study concerned the Mała Wełna river catchment in the hydrological years 2000-2005. The actual values on the day of water sampling and the mean monthly values of water flow were positively correlated (significantly at ? = 0,05) with the concentration of nitrate nitrogen. The relationship was most accurately described with polynomial regression equations. The daily concentrations of nitrates, calculated from the equations, and the daily water flows were used to compute the daily loads which were then treated as a reference. Next, the calculation was made using seven statistical methods, the results were analysed in detail, and a suitable algorithm was selected for computing the annual load at rare measurements of pollutant concentration and frequent measurements of water flow (water levels). The results obtained by calculating the load as a product of the mean concentration of pollutants and the water flow from the interval between the water-sampling dates appeared to be closest to the mean of 2000-2005, computed by reference method (1.00 kg N-NO3 · ha-1 · year-1)

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