As the name implies, there is much soft clay here ("leir" = "clay"), not only in the bay, but also in the grassy fields in over land. The clay was deposited by the Herdla moraine at the end of the last Ice Age, when the sea was 30 metres higher than today. The birdlife is lively on the grassy marshland: the Grey Goose both nests here and uses the area for moulting and resting. Annually, 2-3 pairs of Ringed Plovers nest here, as the only place in the lowlands of Hordaland with the exception of Herdla. The populations of Waxwing and Red Shank are also good. Such areas will probably also attract many unusual bird species during migration time. The cultural landscape inside is rich in passerine species, such as the Linnet and Barn Swallow, and as recently as in 1999, one could hear the rare Corncrake playing here.
Botanically, this marsh is not very diverse, but it has its own distinctive character. Norway sedge is a characteristic species in the swamp environment where remnants of the tidewater remains in pools until it partially or entirely evaporates. Also seaside alkaligrass manages to do well here. It grows quickly, with long creeping shoots and does its bit to keep the clay stable. In this way it also creates a good basis for the growth of such plants as brackish-mud rush, lesser sea-spurrey and slender spike rush.
