[2] For the majority of its 70 miles (110 km) course[3] it flows in a south-easterly direction through Dumfries and Galloway and then into the Solway Firth at Airds Point.

[2] The territory through which the river flows is called Nithsdale (historically known as "Stranit" from Scottish Gaelic: Strath Nid, "valley of the Nith").

In Scotland this does not generally make a significant difference, except for rivers draining into shallow sloping sands of the Irish Sea and Solway Firth, notably the Nith.

[4] The estuary of the River Nith is an internationally important winter feeding site for waders, geese and other wildfowl,[5] and is for this reason protected at an international level as part of the Upper Solway Flats and Marshes Ramsar site and Special Protection Area.

[6][7] The SPA supports virtually the entire Svalbard population of barnacle geese during winter.