Over the last dozen or more years, many applications of vision-based positioning and navigation near the sea bottom and surface have been explored. Mid-water operations have primarily relied on traditional positioning systems, namely INS, DVL, gyros, etc. This paper investigates the application of a vision system for mid-water operations by exploiting stationary features within the water column. The unique nature of these environment-namely, the abundance of randomly distributed targets over a wide field of view and range of depth-are ideal for the application of well-known motion vision methods for 3-D motion estimation and scene analysis. We demonstrate through experiments with water tank and ocean data how various visual motion cues may be used for passive navigation, environmental assessment and target/habitat classification based on visual motion behavior.