In this paper we have analyzed the effects of propagation caused by a curved and rough ocean surface on the lightning generated radiation fields. In the analysis the electromagnetic fields and the return stroke spectrum was computed from a return stroke model recently introduced by Cooray <1993>. The results show that for frequencies higher than about 10 MHz the attenuation caused by the rough ocean surface is significant and, in the worst cases, the peak of the derivative of the radiation field can be attenuated by about 35% in propagating 50--100 km distance over a rough ocean surface. Comparison of the calculated spectrum with the experimentally observed spectrum show that some of the features in the measured spectrum can be accounted for by the propagation effects.