The Colne Valley Regional Park is 43 square miles of parks, green spaces and reservoirs alongside the often multi-channel River Colne and parallel Grand Union Canal, mainly in Hertfordshire and Buckinghamshire, with parts in the London Borough of Hillingdon, Berkshire and a small area in Surrey.
High Speed 2 will pass through the park on a viaduct. In October 2017, activists set up a protest camp at Harvil Road to oppose the construction of the 2.1 miles long Colne Valley Viaduct for High Speed 2. The activists documented alleged environmental damage by HS2 workers over an eighteen month period, voicing concern about the destruction of wildlife habitats and the possibility that an aquifer supplying drinking water might be affected. In May 2019, the Woodland Trust called for the clearance of trees at Colne Valley to be halted. A prosecution against two women for aggravated trespass collapsed in July 2019 because HS2 Ltd could not prove it owned the land in question. In January 2020, HS2 began evicting the protest camps.