Porsnes Lock is a historical landmark located on the Tista River in Halden Municipality, Østfold County. The Tista is the main river in the Halden River Basin, which extends over a total length of 149.5 km. The river is less than 5 km long from Femsjøen to Iddefjorden, and has a catchment area covering 1,584.24 km².
The average discharge at the mouth of the Tista is 22.34 m³/s. The river previously served as the border between the municipalities of Berg and Idd. Porsnes Lock is centrally located in this area, and the river flows peacefully past, which contributes to the historical and scenic value of the place.