A floodwater barrier for protecting the shore side of a shoreline from flooding includes at least one self-actuating floodwater barrier unit for installation between a pair of walls transverse to a shoreline. The unit includes a flexible resilient panel, a plurality of rigid members connected to the panel, at least one watertight chamber of size and arrangement to give the unit water buoyancy, hinged to be rotatable upward about a horizontal axis longitudinal to the shoreline under the influence of buoyancy and hydrostatic pressure from a rise of the body of water acting on the unit, and further includes flexible tension members positioned to act on the floodwater barrier unit to limit upward rotation of the unit to a predetermined extent.