The publication deals with changes in major physical and chemical parameters of water in the Slup dam reservoir, that took place within 1984 - 2000/2001. The reservoir is situated on River Nysa Szalona. Water of the Nysa Szalona, its tributaries, and the Slup were examined at monthly intervals within February 2000 - August 2001. The Nysa Szalona water supplied to the Słup was found to be twice as nutrient-rich at present as it was in the 1980s. The reservoir water contains higher ammonium concentrations. Mean values of trophic state indices in 2000/2001 were lower than those recorded in 1984/1985.