A liquid barrier system automatically deploys when a predetermined liquid level is attained, thereby preventing water or other liquid from entering a structure through an accessway, and automatically retracts when the liquid level recedes. The liquid barrier system includes a float housing assembly installed substantially below grade and adjacent an accessway to a structure. The system also includes a float assembly having a float which is positionable within a float housing relative to a liquid level in the housing. A barrier assembly includes a barrier interconnected to the float, and one or more seal members disposed along a periphery of an accessway. In a high water event, the float rises with the liquid level in the float housing thus causing the barrier to automatically deploy into a sealing engagement with the seal member(s) along the periphery of the accessway, thereby preventing the entry of fluid into the structure.