The Lido Boom and Bust: Britain's Open-Air Pools, 1815 to 2026

Britain's open-air swimming pools are usually described in three acts: a boom of municipal lidos in the 1930s, decline and closure from the 1970s, and a revival driven by local campaigns. There is, however, no open national dataset against which to test that story. I build one from open sources: a register of 73 lidos and open-air pools whose dates or fate can be documented from English Wikipedia text, Wikidata and OpenStreetMap, each entry citing its evidence, together with an inventory of 112 open-air pool sites in OpenStreetMap. Of the 49 register pools with a documented opening year or decade, 33 (67%) opened in the 1930s, 9 in 1935 alone. Of 24 dated closures, 19 (79%) fell between 1970 and 1999, after a median of 61 years of use. Of the 33 pools of known fate that closed at some point, 14 (42%) reopened, 12 of them after 2000, after a median of 7 years shut. Combining the register with OpenStreetMap places 82 working open-air pools, lidos and tidal pools in the UK, 60% of them in London, the South East and the South West and 44% within 2 km of the sea. The register is a documented sample biased towards survivors, so it understates the decline and overstates the comeback; the timing of openings and closures is its most robust result. The data, code and an interactive map are openly available. Register derived from English Wikipedia (CC BY-SA 4.0), Wikidata (CC0) and OpenStreetMap (© OpenStreetMap contributors, ODbL); every entry cites its source. Interactive version: https://tristan-hotham.github.io/lido-boom/. Data and code: https://github.com/Tristan-Hotham/lido-boom. Blog post: https://blog.tristanhotham.com/2026/10/28/lido-boom/.