In this paper the effect of a coastline on radio wave propagation is analyzed. The coastline consists of a shoreline or land/sea transition in the presence of a cliff or bluff. The problem of diffraction from the transition, when excited by a small dipole, is first addressed. By application of a perturbation technique the effects of a gradual, as opposed to an abrupt transition on the radio wave are discussed. For the case of both source and observation near the surface it is shown that the received fields are independent of the gradient of the transition and that the effects of the land/sea transition on the total fields are dominant, even distant from the transition. This is a very important and counter-intuitive result which has not been reported previously. A UTD solution for an impedance wedge and plane wave excitation is then applied, in order to analyze the combined effect of the land/sea transition and a cliff or bluff on the total received fields. Results are shown for the case of an observation platform (such as an aerial vehicle) flying low over the sea and then up and over the bluff.