The reservoir is fed from the Todd Brook, a stream which has a catchment area of around 1,700 hectares (4,200 acres) including the moorland on Shining Tor and farmland around Kettleshulme village.

In August 2019, concrete panels on its spillway were dislodged after heavy rain, triggering the evacuation of parts of Whaley Bridge and the surrounding area due to the possibility of the dam collapsing.

Geological problems continued to dog the project, and the site of the dam was altered on the advice of William Mackenzie in 1837.

In November 1975, low water revealed that another hollow had formed in the same area which led to regular monitoring of the dam.

[2] Repairs were made and a layer of waterproof clay was laid over the weak spot on the upstream face of the dam.

[2][3] In the 1980s, British Waterways carried out significant repair works to deal with leaks involving the mine shafts around the dam and a culvert was constructed under the current beach/launching area of the reservoir.

A stone marker on the main beach showed its location for many years, but was relocated to the footpath opposite Toddbrook Lodge during access work for the 2009 draining.

[13] On 1 August 2019, a major incident was declared and 1,500 residents were evacuated from parts of Whaley Bridge, Furness Vale and New Mills after concrete slabs on the 1969 overflow spillway were partially dislodged by high volumes of water following several days of heavy rain.

An RAF Chinook helicopter dropped 400 tonnes of aggregate into the damaged area[16] and specialist contractors added concrete grouting between the bags of ballast to bind them together to support the spillway.

[18] On 6 August, the Canal & River Trust announced that the aimed reduction in water level of 8 metres (26 ft) had been achieved and that the reservoir was only a quarter full, enabling an inspection of the damage to the structure.

Finally, there will be changes to the inlet from Todd Brook, at the east end of the reservoir, to improve resilience against high water levels after heavy rainfall.

[27] Balmforth was also commissioned to lead a second-stage review, with a wider remit of reservoir safety legislation and implementation.

In parallel with Balmforth's review, the owners and maintainers of the dam, the Canal & River Trust, commissioned Dr Andrew Hughes to seek the reasons for the incident.

His 77-page report stated that "there were indications, that an experienced reservoir engineer should have identified, of the flaws in the design and the potential for a problem to exist and develop.