Since water refraction is completely neglected by some researchers, or it is suggested that it can be omitted by others [15], the effect of it is being investigated in this paper. To evaluate its effect, artificial examples are being used in the scenario of drone photographs.To do so, a scenario is considered, where the effective depth is being calculated by the standard collinearity (Figure 2). Starting from the apparent (erroneous) depth of a point A, its photo-coordinates a1 and a2, can be backtracked in photos O1 and O2, using the standard collinearity equation—the one used for forward calculation of the point’s coordinates, without refraction taken into consideration. If a point has been matched successfully in two photos O1 and O2, then the standard collinearity intersection would have returned the point C, which is the apparent position of point A.According to [10] the two apparent underwater rays A1C and A2C will not intersect except in thespecial case where the point A is equidistant from the camera stations. If the systematic error resulting from the refraction effect is ignored, then the two lines O1A1 and O2A2 do not intersect exactly on the normal, passing from the underwater point A, but approximately at C, the apparent depth of the point. Thus, without some form of correction, refraction acts to produce an image of the surface which appears to lie at a shallower depth than the real surface, and it is worthy of attention that in each shot the collinearity condition is violated [10].