Thieves have targeted Grange-over-Sands Lido, syphoning around £600-worth of fuel and a fuel cube from the construction site.
It happened between 5pm yesterday, January 24, and 7am today, January 25.
The lido and promenade are undergoing a £6.8 million revamp.
Police said it was highly likely a vehicle would have been used for transport of such a quantity and the only access would have been from Grange Railway Station and driving along the promenade.
Anyone with information relating to this incident can report online at www.cumbria.police.uk/report-it quoting incident number 56 of 25/01/24 or call 101.
Alternatively, contact Crimestoppers, anonymously, on 0800 555 111.
