Two anglers in small boats have been filmed dangerously close to a giant "plug hole" at a reservoir.
They were spotted on Saturday a few metres from a 20m deep overflow hole at Derbyshire's Ladybower Reservoir.
Severn Trent Water, which owns the reservoir, warned people boating and fishing there to keep "well away" from the plug hole and to stay safe.
Flo Neilson, who captured the footage while walking her dogs, said the anglers' actions looked dangerous.
"It appeared they were floating towards the plughole whilst still casting their lines, but they were purposely paddling with flippers on their feet," she said.
"It looked a dangerous and risky thing to do, but they seemed to be in control of the boats and had soon moved away after I'd stopped filming."
Severn Trent Water said the plugholes led to a 66ft (20m) drop into a tunnel carrying water to the river through a grill, and warned that anyone who fell in could get seriously injured or trapped.
The firm said: "We're happy for people to use our reservoir for boating and fishing, and boats are available to hire from the fishery.
"However, we do ask that people stay well away from the plug hole, as obviously this is really dangerous.
"We will be reminding everyone who uses the water to avoid the plug hole area and stay safe."