That's why so stimulating to shoot Mergansers! They have the 6th sensory organ and are alert all the time. I usually can get 15-30 meters close to them. In extremely cold days when the lake is almost completely frozen, there may be one or two spots left with water. You can get relatively close to them, only if you are behind such those as reeds. Another way is to find some small streams. When the lake are frozen, the small river is usually OK. I was walking up and down a half mile long stream several times in snow.I saw a kingfisher as well but unable to get close to it.
In birding, getting close to it is harder than aiming at it.
