In a study of human perception of the appearance (clarity and colour) of rivers and lakes for bathing and aesthetic water use, we have shown that: bankside observers can reasonably accurately assess colour (hue) in some circumstances; and that the phenomenon of perceptual set (seeing what is expected to be seen) may influence the visual perception of some waters. Further, perceived naturalness of a water seems to provide for a more positive response towards a water body than might otherwise be expected.