Derbyshire Police revealed it had changed the colour of the water in the disused quarry near Buxton after reports of people congregating there.
The force said it hoped the move would make the “picturesque” site “less appealing” to visitors.
Sharing photos of officers standing near the water in full body protective suits on Wednesday, the force wrote on Facebook: “Yesterday we received reports that people were congregating at the ‘Blue Lagoon’ in Harpur Hill, Buxton.
“No doubt this is due to the picturesque location and the lovely weather (for once!) in Buxton.
“However, the location is dangerous and this type of gathering is in contravention of the current instruction of the UK government.
“With this in mind, we have attended the location this morning and used water dye to make the water look less appealing.”
Police often dye the water in the former limestone quarry black to deter swimmers from entering.
Despite the pool having a pH level of 11.3, making it almost as toxic as bleach and ammonia, many people still flock to it.
Signs have been put up around the site by the council in recent years to warn people the water contains car wrecks, dead animals, excrement and rubbish.
Derbyshire Police has already faced criticism this week for using drones to track people visiting the Peak District after the government imposed a nationwide lockdown on Monday.
The force released a 90-second video showing about seven vehicles in a car park near Curbar Edge in the national park, as well as people in pairs enjoying a stroll and walking their dogs.
It said daily exercise “should be taken locally to your home” and “under government guidance all travel is limited to essential travel only”.
Former justice secretary David Gauke was one of a number of people to criticise the move on Twitter.
He wrote: “This is badly misjudged. People should maintain social distancing, which is what these people are doing.
“We need to maintain public support for fundamental behaviour change which requires the authorities to focus on genuinely bad behaviour.”
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