A barrier for stopping unwanted watercraft and subsurface intruders from entering into a port or off-shore structure is provided. In one embodiment, the invention is a barrier comprised of a vertical net structure supported from the sea floor. The barrier comprises vertical supports and a net assembled between the vertical supports with a system of ropes and energy absorbing devices. The structural components of the barrier are designed and configured in a manner as to absorb and displace the kinetic energy generated by an explosive laden small watercraft traveling at a high rate of speed. In another embodiment, invention is a barrier system installed around the perimeter of a water side or offshore facility. This barrier system comprises a bottom founded perimeter fence having a gate system and a series of barriers comprised of a vertical fence structure supported from the sea floor. This barrier system is designed to control access and to protect a water side or offshore facility from potential terrorism threats.