As standing wave ratio rises, so does the loss in the transmission line. This is caused by:

When the standing wave ratio (SWR) increases, it means that power is being reflected back from the antenna down the transmission line. This reflected energy creates standing waves with areas of higher voltage and higher current than would exist with a perfectly matched line. These increased currents and voltages cause more energy to be dissipated as heat. The higher currents increase resistive losses in the metal conductors (I^2R loss), while the higher voltages increase losses within the insulating dielectric material separating the conductors. Other options are incorrect because antenna currents or voltages do not directly cause transmission line losses, and power does not "leak to ground" through a properly intact dielectric; it is instead converted to heat.