One of the UK's toughest athletic events is taking place in rural Dorset and Somerset with up to 10,000 spectators descending on the area.
Up to 1,500 athletes began the race with a 2.4-mile (3.9km) swim
The Ironman UK Triathlon began at 0800 BST on Sunday, two hours later than scheduled after mist delayed a 2.4-mile (3.9km) swim in Sherborne Castle lake.
The 1,500 athletes are also competing in a 112-mile (180km) cycle race and a 26.2-mile (42.2km) marathon.
The event is the UK qualifier for the world championships in Hawaii.
Half-ironman events have been held locally in the past, giving the area a £4m boost to the local economy, but Sunday's triathlon is the area's first full competition.
Swimmers take refreshments as they run from the lake
Road closures were in place from 0900 BST to 1700 BST for the cycling event and from 1130 BST to midnight for the marathon run.
The cycling route takes competitors from Sherborne Castle along the A352 to Dorchester, back up through the Piddle Valley and into Somerset before returning to Sherborne.
The running takes the athletes along the A30 from Sherborne to Yeovil, up to Montacute House, before they head back to the start/finish point at Sherborne Castle.
A cyclist is handed a banana from a steward during the 112-mile ride
Earlier, John Peake, chairman of Dorset County Council, said: "We are delighted that this hugely challenging and exciting worldwide event is taking place in Dorset and Somerset.
"This is a beautiful part of the country and the event will be an excellent showcase for our area, when we welcome the competitors, their supporters and spectators who will be coming from all over the world.
"To safely host such a fast-moving sporting contest, a number of roads will have to be shut but we are working to ensure any disruption is kept to a minimum and keeping in close touch with the parish councils involved."