Water around the blade should be relatively calm during a paddling stroke. The blade, relative to the water, should have minimal movement, meaning little aeration/ventilation (whirlpools and bubbles), and almost no splash.
At the catch the blade should be pushed into the water, completely submerging the blade, before applying power. During the power phase the blade should be submerged and as vertical as possible through out the stroke. At the end of the stroke the blade should be removed without power, slicing out of the water, rather than lifting and splashing. Overall the stroke should be quiet causing minimal turbulence, whirlpools, and splashing.
The video below provides an idea of an efficient stroke along with a comparison to a less efficient stroke.