The Floating Harbour gave the port an advantage by enabling shipping to stay afloat rather than grounding when the tide went down. Downstream of central Bristol the river passes through the deep Avon Gorge, spanned by Brunel's Clifton Suspension Bridge, the river is tidal and is navigable by seagoing vessels at high tide but drying to a steep sided muddy channel at low tide. It was largely the challenge of navigating this section that sealed the fate of the Floating Harbour as commercial docks and saw them replaced by docks at Avonmouth where the Avon joins the Severn Estuary.