Two people have died in separate incidents which have prompted fresh warnings over the dangers of swimming in open water.
A 16-year-old boy, from London, and a 41-year-old man, from King's Lynn, died in unrelated incidents at Bawsey Pits, a series of flood quarries in Norfolk, on Tuesday night.
Despite the tragedies and dozens of signs warning of the dangers, members of the public could be seen swimming at Bawsey Pits on Wednesday afternoon.
Norman Melton, visiting the lakes from Wisbech, Cambridgeshire, said:
Police said that people had attempted to swim in the lake even as Tuesday's rescue attempt was under way.
The man had told his girlfriend he planned to swim about 50 yards (45m) out in one of the flooded quarries towards an island. He was near the shore of the island when he disappeared below the surface.
At the same time, police were told of the missing teenager at another lake about half a mile (0.8km) away. After searches were launched at 4.30pm, the body of the man was found at 7.24pm and the teenager at 9.25pm.
Both were found entangled in reeds about 6ft (2m) below the surface, Norfolk's chief fire officer Nigel Williams said.
Hundreds of sunbathers looked on as the search took place and Mr Williams said officers had to prevent members of the public entering the water.
He added: "It was an extremely hot day and clearly the temptation to enter the water, despite many warning signs, was too much for some. When we arrived there were people still swimming in the water, oblivious to what was going on.
"Swimming is banned here and the signs are there for everybody to see. This just highlights the dangers of swimming here or in any other unsupervised area of open water.
"We don't know if they were dragged under by some obstacle or other but they were certainly held below the surface by reeds. It is difficult to say how long they could have survived, but we were battling against time and they would only have survived for minutes."
A spokesman for Sibelco, which runs the disused quarry, said it was deeply saddened by the deaths.
He added: "Safety is our prime concern and signs are in place to warn against swimming and diving. We will work with the police and other investigating authorities to help establish exactly what took place. Until that process has run its course, we can only say further that our thoughts go out to all who have been touched by these deaths."