Cardiff in making iron and later steel, brought to the sea by packhorse from Merthyr Tydfil. This was first achieved by the construction of a long canal from Merthyr (510 feet above sea-level) to the Taff Estuary at Cardiff. Eventually the Taff Vale Railway replaced the canal barges and massive marshalling yards sprang up as new docks were developed in Cardiff – all prompted by the soaring worldwide demand for coal from the South Wales valleys. At its peak, Cardiff's port area, known as Tiger Bay, became the busiest port in the world and – for some time – the world's
Cardiff Bay Barrage 85% to 78% as a result of lower levels of winter survival. The freshwater lake had problems with blue-green algae initially which made it impossible to swim in the water or participate in water sports. These issues have now largely been resolved though some toxic algae remain in some of the dock areas in the bay. 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. The Cardiff Harbour Authority has decreed that "Personal watercraft" used