Lake Isesjø is tributary to the Glomma water system, emptying into the Nipa River at Hafslundsøy in Sarpsborg. A medium large lake, it is surrounded by forest and open landscapes in an interesting area east of Sarpsborg. Most of the area around the lake is forested, but there are large sections of cultivated land facing the lake in the northern and southern parts.
Lake Isesjø is located 30 metres above the sea and has an average depth of around 9.5 m with 22 m the deepest point. The lake sports several coves, points and underwater reefs – all excellent fishing sites for most species.