Otters do not see that well, especially if you try to blend in with your surroundings. But I never wear camouflage and never use a blind. It's best to be mobile when watching otters. Otters rely on smell and hearing. Once I went out with someone with perfume. Otters over 100 yards away got alarmed. Once I snapped a stick, and otters went into a tizzy to escape. (Then again once a whole second grade class came down to a pond and the otters in it looked at them with great curiosity.)
I try to keep something close behind me, like a tree trunk or pond bank. I was on a relatively shady bank looking down at this little otter, and that mid-body twitch shows that it saw me. Eventually the mother would make clear that she noticed me, but what she did was simply gather the pups together and leave. Remember the video of the otters fishing right below the rock? The mother swam in and with a few chirps to the pups and snorts at me, led the otters away. Turn the page: page26