The River Calder is a river in West Yorkshire. It starts above Todmorden, and drains an area of 369 square miles (957 km²). It joins the River Aire near Castleford

Only a few bits of the river can be used by boats but they are connected by the Calder and Hebble Navigation, a popular leisure waterway which is part of the connected inland waterway network of England and Wales.

Many woolen mills were built along its banks, particularly at Dewsbury and Wakefield, but also in the smaller towns of Brighouse, Hebden Bridge, Sowerby Bridge and Todmorden. It used to have salmon, but they were killed by pollution in the mid 19th century. In 2008 they were seen again.^[1]

At Wakefield's there is a nine-arched bridge, 320 feet (98 m) long, built in sandstone between 1342 and 1356.