Calculating water reflection y-coordinates of birds/clouds in a 2d landscape

I am having trouble to calculate the y coordinate for the water reflections of birds/clouds in a 2d landscape. So I think some factors that determine the y_relection are the height (y) and depth (z, although I haven't used 3d) of the cloud/bird and also the viewing angle (but again this is all just 2d drawn sprites). Anyone an idea how I could proceed to calculate the y_reflection in this 2d setup?