Tjele Langsø near Viborg is 8.5 km long and thus one of Denmark's longest lakes. The catchment area of the lake consists mainly of agricultural areas as well as forests and lakes.
Tjele Langsø is a deep and nutrient-rich lake that flows into the Hjarbæk Fjord through the Vorning Å and Skals Å. The water temperature during the summer period ranges from about 1 to 22 degrees Celsius.
Tjele Langsø is located in the remains of a long, elongated tunnel valley that originated around the Mariager Fjord. The tunnel valley joins a more northerly tunnel valley around Viborg, from where meltwater streams continued to the Hald Sø area. From there, the water flowed further out over the Karup Hede plain.