The 29.4 hectare protected area of Kalvø-Hasselø was created by Conservation Order in 1980,[1] and access is prohibited during the bird breeding season.
Today, with its grassy expanses and waterholes of various sizes, it is used for grazing young cattle during the summer months.
Access is forbidden from 15 March to 15 July when birds are breeding and raising their young.
On the other hand, it is not easy to transport them to the island or to carry out the regular checks that are required.
There are also risks of the animals contracting mastitis which can be borne by insects attracted by the watery area.