Abstract: Study on the physico-chemical properties of Ero reservoir, a tropical reservoir situated in Ekiti State, Southwest Nigeria, was carried out between April 2003 and March 2005. Monthly variations were observed in the parameters measured. During the period of this study, ranges of parameters were: 24.2 and 29.2�C for temperature; Turbidity 38.0-49.9 cm; pH, 6.8-7.7 and D.O, 4.7-5.2 mg L 1. Generally, the ranges of these parameters fell within optimum limit for fish production.