I've been lucky to have a resident pair which patrolled my usual stretch of river, when I lived in Sweden (the Ljusnan river at that point is shallow and about 250 yards wide). You'd see them (one at a time) go in a regular pattern, hunting upstream, and they'd get a fish on every third 'beat', on average. They didn't often get trout but took mostly what the Swedes call 'sik' which is a salmonid, a little like a cross between a grayling and a chub.
It's great having a natural hunter showing you where the hot spots are
Apart from that, there were otters, cranes and beavers galore...