The clay horizon in the Holtingerveld causes rainwater to accumulate on the surface. This causes layers of water to be permanently present on the surface. Places where there is no boulder clay in the soil can also be soaking wet. This is because a small layer of iron or vegetable matter is present in the soil. Here too, fens and ponds emerged. Some fens originate from the last ice age. The topsoil was permanently frozen in that time. The ascending ground water reached the frozen layer from the underneath and created a giant hump of ice that way. Once the soil melted again, a water-filled depression remained.

A wide variety of special plants grow in these fens, such as floating water-plantain. The water’s edge is often lined with a zone of raised bog, which is home to all kinds of plants, such as peat moss, cranberries and white beak-sedge. Water birds such as the black-necked grebe and the common teal are also breeding In the ponds and fens. The many dragonflies foraging along the water’s edge will certainly catch the eye.