Completed in 1999 at a cost of £220 million, this large dam plugged the gap between Penarth and Porth Teigr, containing the waters flowing out from the mouths of the Rivers Taff and Ely, and transforming stinky Cardiff Bay into a freshwater lake. It includes sluice gates to control the water flow, three lock gates to allow passage for boats, and a fish pass that lets migrating salmon and sea trout pass between the rivers and the Bristol Channel.
When it was built, the barrage was a controversial project, as its construction flooded 200 hectares of intertidal mudflats, which, despite their unpleasant aspects, were an important habitat for waterfowl.
A walking and cycling track heads out over the barrage, providing easy access to Penarth (allow 40 minutes if you're walking). This is part of the Bay Trail, a 6.2-mile walking and cycling loop that follows the shoreline back to Butetown. Along the way there's a skate park, a playground, some giant boulders of coal, and a series of display boards telling the story of Captain Robert Scott's expedition to the Antarctic, which set sail from Cardiff in 1910. Two years later Scott and his men were dead, having been pipped to the pole by a Norwegian team led by Roald Amundsen.