It is related to other, less rare, water beetles of The Netherlands.
It lives in peat bogs and fish ponds.
It is mainly active at night.
It is the biggest carnivorous water beetle of Europe.
It can be over 4 centimeter long.
Since 1967, it had not been seen in its last bulwark in Dutch waters, Drenthe province.
However, in October this year, a Dutch student found it again in that province after all those years.
Source: daily NRC, 24 November 2005.
See also here.