Recently NO3-N concentrations of the rivers that flow into the Kasumigaura lake have increased. The lake is much eutrophicated and is used as a source of water supply for Tsuchiura-city. Stocking density and NO3-N specific load have a high correlation (r=0.93). NO3-N concentrations increase corresponding to the increase of stocking density. In this area the livestock has a larger influence to the nitrogen concentration of the rivers than the land use.