Conditions are obtained for the existence of a fast-moving surface electromagnetic wave (with a speed close to the speed of light in the vacuum) on a flat interface between the vacuum and an isotropic dissipative medium with a permittivity ε = ε′ + iε″. The interfaces considered include vacuum - sea-water, vacuum-metal, vacuum-plasma, and vacuum-dielectric. Conditions for the existence of negligibly damped surface waves are considered for extremely high (vacuum-seawater, vacuum-metal) and very low (vacuum-plasma, vacuum-dielectric) ε″ values. It is shown that at least in these two limit cases, the phase wave velocity V_p and the group wave velocity V_g pass synchronously through the speed of light c in the vacuum, which can be considered the reason why surface waves exist at the interface between the vacuum and a collisionless plasma (with ε′ < -1 and V_(p,g) < c) and do not exist at the interface between the vacuum and a weakly absorbing dielectric (with ε′ > 1 and V_(p,g) > c). In the first limit case, it is shown that both the phase and group velocities pass c at ε′ = -3/4, implying that a surface wave exists at the vacuum-metal interface (with ε′ < -3/4), but that a surface wave (Zenneck's wave) cannot exist at the vacuum-seawater interface (with ε′ > -3/4).
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