The origin of the scheme dates back to a visit by Nicholas Edwards, the Secretary of State for Wales, to the largely-derelict Cardiff docklands in the early 1980s.

However the tidal nature of Cardiff Bay, exposing extensive mudflats save for two hours either side of high water, was seen as aesthetically unappealing.

The development was also inspired by the redevelopment of Baltimore Inner Harbor in the US, where a largely derelict port area was transformed into a thriving commercial district and tourist attraction.

In November 1999, the barrage was completed, with the sluice gates closed at high water, to retain the seawater from the Bristol Channel within the 500 acre (200 hectare) bay.

At first major water quality problems ensued which required the bay to be drained dry overnight and refilled each day.

One of the most prominent critics was the then Cardiff West Member of Parliament (MP), Rhodri Morgan (Labour), who was later to become First Minister of the Welsh Assembly.

In the meantime, local residents living near the edge of the bay and the banks of River Taff feared that their homes would be damaged by the permanently raised water level, as they had been in several previous floods.

Concerns were also raised over groundwater levels in low-lying areas of Cardiff possibly affecting cellars and underground electrical junctions.

The bill included provisions for compensation for any homes damaged by the barrage and a large wetland habitat for birds further east down the Bristol Channel.

Features include a fish pass to allow salmon to reach breeding grounds in the River Taff[6] and three locks for maritime traffic.

This would not only enhance tourism on both sides but provide a pleasant and safe short-cut between Cardiff and Penarth, cutting two miles off the journey otherwise taken on the heavy-traffic roads further upstream.

However, this benefit took years to materialise due to a lack of agreement between the derelict access land owners (Associated British Ports) and Cardiff Council.

According to two studies published in 2006,[11] the loss of intertidal mudflats has resulted in the numbers and diversity of the birds using Cardiff Bay greatly reducing.

[12] Cardiff Bay has become the first area of freshwater in Wales to be infested with zebra mussels – an alien species to the UK which multiplies rapidly to the detriment of native marine life.