Cardiff Bay: dolphins

Dolphin: Naut.; a post or buoy for mooring a vessel (Collins Dictionary).

The Environment Agency, a division of the UK Department for Environment Food & Rural Affairs, provides this rather more comprehensive definition as part of its asset management information:

A man-made marine structure that extends above the water level and is not connected to shore. It is usually piled into the river or sea bed. Dolphins may be used as a temporary tethering point, a structure for housing navigation aids or for protecting other structures from ship impacts.

The old timber dolphins dotted around Cardiff Bay, near Mermaid Quay and the entrance to Penarth Marina, serve as a reminder of the days when Cardiff was a very busy port, when ships from all around the world would be moored not only at the quay sides but also to the dolphins, awaiting their allocated slots for unloading and reloading. Some of these dolphins are now in a very dilapidated state, while others continue to carry functional navigation aids for the marine traffic still active within the Bay.