The northern Dutch city Leeuwarden (in the province Friesland) has an otter park called Otterpark Aqualutra. The special animal can be examined from close range here. The partly educational centre tells you that otters are the ambassadors of fresh water environments: if otters are leaving a certain region in masses, it shows that the fresh water has been polluted in any way.
The address in case you happen to be in the neighbourhood: Otterpark Aqualutra, De Groene Ster 2, Leeuwarden. Its website at http://www.aqualutra.nl is only in Dutch but packed with photo's of otters and similar animals.