A culvert beneath the canal collapsed, said British Waterways Enlarge Image

Thousands of litres of water escaped on Wednesday along 1.5 miles of the Monmouthshire and Brecon Canal near the village of Llangynidr near Brecon.

British Waterways said its engineers were investigating what caused the culvert to collapse, and were also assessing the scale of the damage.

Officials said no canal boats were affected by the problem.

British Waterways said it had put up waterside notices to inform boaters about the closure, and was also contacting canal-side businesses.

A spokeswoman said: "British Waterways, which cares for the canal, was notified during the morning of 17 January that a culvert beneath the bed of the waterway had collapsed, allowing water to escape from the canal channel and run into the adjacent River Usk."

A three-year restoration project ended in 2005

She added that the canal and its tow path was closed between bridge 122, two miles west of Llangattock, and bridge 129, near the village of Llangynidr.

The stretch of waterway re-opened for the first time in 60 years following a three-year restoration project in 2005.

A small army of volunteers, many from across Europe, helped return it to a working canal route.