Fishing license - Fishing license Everyone between 18 and 65 years old must have a fishing license to fish in public, salty or fresh waters. Fishing signs can be purchased at post offices as well as a number of tourist agencies, campsites and at several of the Danish Troopers' members. If you want to fish in the river or in a lake, you must have a fishing license for the fishery in question. Public fishing signs are not required for a trout lake or Put & Take water.