Every time I watch a movie where something is coming out of the water, it always does so slowly. Sliding or crawling up and out of the water, onto the lake or river bank, slowly moving toward the intended victim.
As demonstrated by a baby Cthulhu I'm not sure that's how that would actually happen.
There was a shark movie that had the s hark leap out and eat Samual Jackson's character that quick. Can't remember it off hand.