One of the best traits of otter are that they are not timid around people. They might swim up to you to get a better look at you, often when they are swimming away, they will pause and look back in shallow areas (see photo below).
Otter are a fast moving subject and a bit unpredictable. This is handheld shooting and my 100-400mm zoom lens seems ideal. Stabilization and a fast shutter speed are important. I usually shoot ISO 2000 and wide open. Because they are a dark subject, I will overexpose to get texture in their shiny wet fur. When you visit the valley to see the elk, you must stop and check for otter. If you see them, stop and shoot a while, you may never see them again.
|River Otter Buffalo National River pausing to look back.|