The use of the filter would allow the sky to be a slightly darker, to match the richness of the reflection. If you look at the last three reflections, you'll notice that the reflection is slightly darker that the source. Water acts as a natural filter for some of the light. If you want a balanced image, the graduated neutral density filter is a great tool.
Shooting for Success: Hit-and-Run Photography
Next we have a shot came across while driving with a friend along the Trans Canada Highway from Lake Louise to Banff. Just before we reached the Banff turnoff this is the sight we saw.