Following the end of coal mining locally, the Dearne Valley had become a derelict post-industrial area, and the removal of soil to cover an adjacent polluted site enabled the creation of the wetlands at Old Moor.

[1] The area has been settled continuously since prehistoric times, with villages developing on the drier sandstone ridges above the flood plain from at least the late Saxon period.

This connected Barnsley to the River Don and beyond, aiding the intensive exploitation of the locality's coal, sandstone and iron ore. Over the next two centuries, especially following the arrival of the railway in 1840, the area became dominated by its heavy industries.

[7] The miners' strike of 1984 was the first sign of a national programme of pit closures in the UK that led to all the Dearne Valley mines being closed by 1993, with the loss of 11,000 jobs in the industry.

About 600 hectares (1,500 acres) of the former Wath Manvers Colliery, including a coking plant and marshalling yard, was left as the largest derelict site in western Europe.

The Royal Society for the Protection of Birds (RSPB) suggested adding reed beds to help the then-struggling bittern population;[4][7] only 11 males were present in the UK at one point in the 1990s.

The RSPB had changed it its position since its refusal in 1997, with a greater emphasis nationally on engaging the public, and more opportunities to work with the Environment Agency to create and manage new wetlands.

With help from the Environment Agency, local councils and others, the RSPB tripled its land holding in the area to 309 hectares (760 acres) in the next ten years, while other conservation bodies also created and improved reserves.

[15] The reserve has a visitor centre, created by Barnsley Council from existing farm buildings,[7] which includes a shop, educational facilities, a café and toilets, picnic and play areas and nature trails.

[15] Old Moor was planned as an "Urban Gateway" RSPB site, its playground, café balcony and children's discovery zone intended to attract visitors.

[18] The main focus on management throughout the Dearne Valley complex is on its key habitats: wet grassland, open water and reed bed.

Bringing fertile mud from Blacktoft Sands RSPB reserve has helped, although the reeds still stand in ribbons rather than solid blocks.

[7] Since the 1990s the RSPB has been attempting to create improved habitats for the formerly endangered UK bittern population, with major reed bed creation at their Ham Wall and Lakenheath Fen reserves being a key part of the bittern recovery programme initiated in 1994 as part of the United Kingdom Biodiversity Action Plan.

[22] At Old Moor, in addition to the creation of new reed beds, 23,000 small fish were introduced between 2010 and 2016, mainly of species such as rudd and eels that are preferred as food by bitterns.

[7] The post-industrial landscaping and planting in the area have created a suitable habitat for the species containing willow, alder and clumps of bramble close to water and linked by linear features such as railways, canals and streams.

Lesser noctule bats and water voles figure among the scarcer mammals found on the reserve, and otters have returned to the now-clean rivers.

Nationally scarce nocturnal moths include the cream-bordered green pea and chocolate-tip, while the red-eyed damselfly and red-veined and black darters are notable among the Odonata.

[7] Several rare flies have been recorded, including three species, Parochthiphila coronata, Calamoncosis aspistylina and Neoascia interrupta, otherwise known in the UK only from a few sites in the East Anglian fenland.