Long Moor Beck flows eastwards and joins as the Little Don enters Swinden Plantation, and the moorland scenery gives way to woodland.

The river loops to the north, where it is joined by Great Grain, and passes over a weir to enter Langsett Reservoir.

Sheffield Corporation bought the site in 1898 (or 1889 - sources vary) from the Pilkington family, and also purchased a number of local farms which were then abandoned, in order to prevent contamination of the water supply.

It was officially opened on 17 October, and held the largest volume of water of the dams constructed in the Sheffield area.

[3] Transport of materials for the construction was aided by the Sheffield Corporation Railway, which ran along the north bank of the river from Stocksbridge.

[4] The dam crossed the valley at the eastern end of the reservoir, and Midhope Cliff Lane ran along the top of it.

[6] A little further downstream, the Little Don is joined by Hagg Brook, a small stream that is fed by the overflow from Midhope Reservoir.

[2] This small bridge carried Mortimer Road over the river, and is constructed of coursed gritstone blocks.

It opened on 14 April 1877, and passenger services, which were mainly used by workers at the steelworks and pupils from Penistone Grammar School, ran until 1931.

The river system has not been classed as good quality because of sewage discharges and physical modification of the channel, which restricts the movement of fish.

Like many rivers in the UK, the chemical status changed from good to fail in 2019, due to the presence of polybrominated diphenyl ethers (PBDE), perfluorooctane sulphonate (PFOS) and mercury compounds, none of which had previously been included in the assessment.

As well as barriers to the movement of fish, the river has also been affected by pollution from minewater and by the presence of the invasive species, the New Zealand mud snail.

There is a small amount of minewater which does not get processed by the plant, and a solution for this is being trialled by the Environment Agency, Yorkshire Water, and Highways England.

[22] In order to provide control data, similar monitoring was carried out at Grimwith Reservoir in North Yorkshire where there are two tributaries with no weirs.