My aquatic biology professor in grad school - a former navy man - would go nuts when we suggested that we were walking on a "dock" or tying our boats up to a "dock". He was quick to point out that the thing you walk on, sit on, fish from, and sometimes tie boats to is called a "pier". The dock is the area of water alongside a pier on which the boat rests.

He used to say that only Jesus could walk on a dock.