Thornton Reservoir became operational in around 1854. The 2.5-mile footpath round the res opened to the public in 1997.
During the summer of 2018 the reservoir levels began to drop by around a foot per week, which co-insided with the 6 week drought during June and July that year. It turned out that the water level was actually being deliberately lowered so that repairs could be undertaken to the nearby overflow (spillway). Works commenced on 7th January 2019. Water levels went up and down throughout both 2018 and 2019 but generally stayed around 6 ft lower than usual.
Works were largely complete when the new spillway and deflection structure were first put to the test after heavy rain between 25-26th October 2019, and around 18 months of not being in use. Its biggest test to date was 16th February 2020 during Storm Dennis, when water poured over the entire spillway - not just the lower central part like usual. This does not happen often at all, the last time I can remember being June 2012 after a storm with giant hailstones and a tornado which passed across Wood Bank at the other side of the dam.
The biggest problem with the cache is likely to be muggle, depending on the time of your visit so try and be discreet when removing/ replacing the cache. You will need your own pen and tweezers or some other extraction device will be needed to extract the log!