I show a lot of River Otter photos on my blog, mainly because I understand and admire their behavior, plus it gives me a great challenge for trail camera photographs. These are very difficult animals for close up photos.
First thing you need is to be able to identify otter sign along the river and ponds. They usually have certain places they go onto the bank and leave scent for other otters to recognize, they are like a big family. These landings, as I call them, can be far apart and unless you place a camera on the landings you may never get an otter picture.
The photos above give several things to look for to identify a landing. First is the blue circle showing the brown moss killed by the otter leaving a urine scent on the rock. This is very common when an otter is just passing through the area. Next is in the red circle showing where an otter left it's scat on the rock. Otter don't really have a stomach but a spiral intestine, they gorge themselves with food and it doesn't digest completely so I can tell what they eat and from that where they have been. Blue gill scales show they have been in a lake, crawfish bones from creeks and rivers and then eels and salmon.