A 500-hectare area along the river, spanning 20 kilometers between Karup and Hagebro, was protected in 1964, and the entire stretch from Karup to Skive, a total of 1,008 hectares (including some tributaries), is now a European Union Special Area of Conservation.

[3] Further upstream, there are tributaries from Vallerbæk, which comes from Kompedal Plantage [da], and a couple of kilometers south of Karup, the river receives an eastern tributary from Haller River, which comes from the area around Hauge Sø [da] near Grathe Heath south of Thorning.

About 10 kilometers northwest of Karup, there is a tributary from Resen Brook at Resen, which, along with the slightly more northerly tributary Sejbæk, drains the Alheden [da] heath and Kongenshus Mindepark [da].

Aakjær often wrote about the river and its significance for the people and nature of the region, and the poem Karup Aa (Karup River) from the 1901 poetry collection Fri Felt examplifies this.

However, in the 1870s, a vast network of canals was constructed for watering the meadows to improve hay production.