A portable, water-filled barrier is internally divided into cells and emulates a sandbag dike or wall without requiring sand or intensive labor to install. Rigid steps spans the barrier to provide structural support and enable traversing of the barrier. The steps can be attachable to the barrier. The light, flexible barrier material can include nanofiber. Automatic valves can seal openings between the filled cells, so that a punctured cell will not cause cells below and behind to deflate. Cells can project below the base into a stabilizing trench. Cells can include internal or external rods or plates that support the barrier structure. Some embodiments can be initially filled with air, positioned, and then filled with water while the air escapes through a pressure valve. Other embodiments are filled from above, and inflate and deflate without allowing air into the barrier. Barrier end structures can enable interlocking of adjacent units.