Børsesjø is located at the northern end of Gjerpensdalen, and is a protected nature reserve.
Over 210 varieties of birds are to be found here and the following species of fish; bream, roach and eel.
Børsesjø is most readily accesabel from Gjerpen Church.
A marked path to the "Fugletårnet" (bird watcher tower) lies between Gjerpen nursing home and the priests rectory.
Access to the reserve is not permitted from the 15th of April to the 1st of July with the exception of the marked path to the observation tower.