The Little Don River also known as The Porter, is a tributary of the River Don in England. Arising on the Langsett Moors in the northern Peak District

Peak District

The Peak District is an upland area in central and northern England, lying mainly in northern Derbyshire, but also covering parts of Cheshire, Greater Manchester, Staffordshire, and South and West Yorkshire....

, the Little Don River feeds the Langsett

Langsett Reservoir

Langsett Reservoir is in Yorkshire, England, near the villages of Langsett and Upper Midhope, on the edge of the Peak District National Park. The reservoir was constructed between 1898 and 1904, and is now managed by Yorkshire Water...

 and Underbank Reservoirs. It runs through StocksbridgeSheffield

Sheffield

Sheffield is a city and metropolitan borough of South Yorkshire, England. Its name derives from the River Sheaf, which runs through the city. Historically a part of the West Riding of Yorkshire, and with some of its southern suburbs annexed from Derbyshire, the city has grown from its largely...

, England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

 before joining the River Don.

A 1.1 hectare section of the river is designated as a site of special scientific interest

Site of Special Scientific Interest

A Site of Special Scientific Interest is a conservation designation denoting a protected area in the United Kingdom. SSSIs are the basic building block of site-based nature conservation legislation and most other legal nature/geological conservation designations in Great Britain are based upon...

 since 1977. The site is of considerable importance as it is a proposed reference example for various subdivisions of the Carboniferous

Carboniferous

The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

. It is one of 35 sites of special scientific interest in South Yorkshire.