Thy National Park comprises a large part of Denmark's total dune area. The dune landscape is dynamic and can hold great variation, even within small distances. The dune vegetation is influenced by physical conditions, such as the drifting of sand, lime content, nutrients, dune slope orientation and distance to the groundwater table.
Different types of dunes are represented in Thy National Park. The national park includes sea shores with incipient dune formation and the white dunes characterised by continued sand drift, as well as the more stable dune shapes such as the calcareous and vigorous green dune and the grey dune with its permanent cover of lichen and dwarf shrubs.
The dune heath
The dune heath is characterised by coherent vegetation of dwarf shrubs. The dune heath is a mosaic of plains and massive dune formations dominated by crowberry and heather as well as sand plains with temporary lakes and wet sand hollows where bell heather, bog myrtle and bog bilberry dominate the landscape. Sand hollows also create a living space for some of the more rare species such as marsh gentian and alcon blue.
The largest dune heaths in the national park are Hanstholm Nature Reserve, Vangså Klithede and Ålvand Klithede as well as the dune heaths between Stenbjerg and Lodbjerg. These dune heaths hold large populations of red deer, otter and adder, and they are breeding grounds for many rare birds such as cranes and wood sandpipers.
Lakes in the national park
There are more than 200 large and small lakes in Thy National Park. Many of them are among the cleanest lakes in Denmark and are habitats for many rare plants. Many of the dune lakes are lobelia lakes. These are nutrient-poor, clear-water lakes with sandy bottoms. The characteristic lobelia dortmanna plant, and often other underwater plants such as quillwort, plantain shoreweed and pillwort, grow here.
Thy National Park also has the large karst lakes Vandet Lake and Nors Lake. These are the only places in Denmark where the slender naiad grows.
In the southern part of the national park are Ørum Lake and the brackish Flade Lake. Both lakes used to be part of Krik Vig inlet. They are very shallow and relatively rich in nutrients.