NATURA 2000 - species and habitats

The brook lamprey spends several years of its life in the form of a worm-like larva in muddy sand in clean rivers. After 5-7 years it transforms into the adult form with an eel-like, extended body. It prefers to spawn in shallow channels in gravel or sand exposed to bright sunlight. As such conditions have become rare, the brook lamprey has become an endangered species in Austria.

additional link https://en.wikipedia.org/wiki/Ukrainian_brook_lamprey