The Balder is an English river that rises on the eastern slope of Stainmore Common in the Pennine Chain and flows eastwards for about 23.4 kilometres (14.5 mi), before joining the River Tees at Cotherstone.

[1][7] The River Balder enters Balderhead Reservoir about 7 kilometres (4.3 mi) from the source, at 336 metres (1,102 ft) above sea level.

The distinctive flat peak of Goldsborough to the south is passed before the valley begins to open out as the river enters Blackton Reservoir at 285 metres (935 ft).

The river now begins to twist and turn and is crossed by the grade II listed, nine-arched Balder Railway Viaduct, which was used by the Barnard Castle to Middleton-in-Teesdale railway line before it was closed.

[11][12] It finally joins the River Tees at Cotherstone, at a height of about 162 metres (531 ft).