Almost the last word.

Water won't flow smoothly between the fingers due to their boundary layers, which act like invisible webbing, thus increasing the effective size of the hand. Even though the surface area may be similar, your individual fingers are more "aqua-dynamic" than the flat paddle that is formed by fingers held tightly together. David Muir Edinburgh, UK Fluid dynamics can be counterintuitive due to the effects of boundary layers. [Extracted from the article]