Husby Sø og Nørresø Nature Reserve: Mapped Protected Landscapes and Wetland Geography in Region Midtjylland

The site is best known for its shallow, stonewort-rich lakes that harbor some of the highest aquatic plant diversity of any Danish lakes, including a large proportion of the country's pondweed species and several red-listed aquatic plants.

The lakes of Husby Sø og Nørresø originally formed part of a maritime landscape connected to Ringkøbing Fjord. Early in the twentieth century, the still-connected coastal basin was gradually cut off from the sea by a major drainage and diking project carried out between 1940 and 1949. The work severed the southern marine connection of the basins, and the new outlet to Nissum Fjord was established through a man-made channel known as Staby Kast. The lakes were subsequently reshaped by inflows pumped from increasingly drained agricultural land.

Formal protection began in 1956, when Nørresø and a 140-hectare area around it were designated as a nature reserve (fredning). The wider lakes and surroundings were later included in Denmark's Natura 2000 network as site number 72, with a habitat-area code (H188). The Natura 2000 plan for the area was adopted in 2011, after which the municipalities of Holstebro and Ringkøbing-Skjern, together with the Danish Nature Agency (Naturstyrelsen), drew up binding action plans to implement the plan. The nature plan has since been reviewed and extended through later planning periods and is coordinated with the water plan (vandplan) for the Nissum Fjord main catchment.

The setting of Husby Sø og Nørresø is defined by flat, low-lying coastal plain terrain typical of western Jutland. The lakes occupy shallow basins on an ancient marine foreland south of Nissum Fjord, an area formed by historic coastal processes rather than by major faulting or uplift. The result is a quietly undulating landscape where open water, reedswamp margins, bog, and meadow merge with surrounding farmland.

Husby Sø and Nørresø themselves are large shallow lakes; their waters are calm and clear enough to support extensive submerged plant growth. Reedswamp belts (rørskov) fringe much of the shoreline, softening the transition between open water and land. Beyond the immediate lake margins, low-lying mose (bog) areas and wet meadows extend outward, creating a varied mosaic of wetland vegetation. The hydrography of the site is human-engineered in key respects: an embankment cuts the lakes off from their original southern marine connection, while water is pumped in from surrounding arable land and discharged via the Staby Kast channel.

Ecologically, the area stands out for the quality of its aquatic and wetland habitats. Four main Natura 2000 habitat types underpin the site's designation: hard oligo-mesotrophic waters with stonewort (kransnålalge) vegetation, nutrient-rich lakes with diverse aquatic flora, lake shores with small herb communities, and calcareous fens (rigkær). Together these classifications describe a freshwater system rich in submerged and floating-leaved plants interspersed with ecologically valuable shore and mire communities.

Biological surveys conducted in 2005 underlined the richness of these habitats. In Husby Sø, 54 plant species were recorded, including 41 submerged species, 6 species of stoneworts, and 7 species of floating-leaved plants. Fourteen of Denmark's nineteen pondweed species were found there, along with three pondweed hybrids. In Nørresø, 25 plant species were recorded, including 19 submerged plants, 2 stonewort species, and 4 floating-leaved species, with 8 pondweed species documented. Many of these species are considered uncommon nationally, reinforcing the lakes' reputation as some of the most botanically diverse in Denmark.

The site's wildlife profile is closely tied to its aquatic habitats. The lakes are home to an extensive community of submerged and floating-leaved plants, including numerous pondweed species and stoneworts, which in turn support invertebrate communities that anchor the local food web. Surrounding reedswamp, bog, and meadow habitats provide cover and feeding areas for wetland-associated fauna beyond the water itself.

The Eurasian otter (odder) is listed among the qualifying species of the habitat area, reflecting the importance of clean water, lakeside cover, and connected wetland habitat for its survival. Many of the recorded aquatic plants are nationally red-listed or on the Danish yellow list of declining species, underscoring that the conservation value of the area is strongly botanical, while the otter presence adds a notable mammal species to its faunal significance.

The conservation significance of Husby Sø og Nørresø lies in its role as a refuge for freshwater habitats and aquatic plant diversity that has become rare elsewhere in Denmark. The lakes hold a very high share of the country's pondweed species and support diverse stonewort and floating-leaved vegetation, marking them out as among the most botanically valuable lakes in the country and a critical holding for several red-listed aquatic plants.

Protection began in 1956 with the fredning of Nørresø and its immediate surroundings. The site was later incorporated into the Natura 2000 network as habitat area H188, and its Natura 2000 plan, adopted in 2011, guides ongoing management. Because the catchment is heavily agricultural and water reaching the lakes is largely pumped from drained farmland, conservation efforts focus on protecting water quality, maintaining characteristic hydrology, and coordinating nature protection with the water plan for the Nissum Fjord catchment.

Unusually high aquatic plant diversity for Danish lakes, including a large share of national pondweed species.

Two complementary shallow lakes, Husby Sø and Nørresø, set within a matrix of bog, meadow, and reedswamp on an old marine foreland.

Habitat area formally protected since 1956 and now embedded in Denmark's Natura 2000 network (site 72, H188).