The main body of the idyllic Lake Øymarksjøen is the Marker Municipality with only small part in the Aremark Municipality. The narrow lake is part of the Haldenvassdraget lake district and has its own tributaries in Otteidvika and Kilesjøen lakes. Towards it southern end the lake broadens to form the Bøenfjorden Bay with many small islands and finally empties into the Strømselva River. Pike fishing is excellent in Lake Øymarksjøen and there are many perch.
Using locks it’s possible to travel to Lake Aremarksjøen, through to Lake Aspern and then on to Lake Femsjøen. The many islands and skerries in Lake Øymarksjøen create a host of fishing sites, mainly from a boat. The largest reed beds are found in northern part, as well as on the western side of the southernmost part.