Police said an underwater search was launched to find a man who entered a body of water over the weekend.
Emergency services responded to reports of two people entering the water at Dovestone Reservoir on Saddleworth Moor, Greater Manchester Police said in a statement just after 3.30pm on Sunday.
One person was saved and helped by paramedics.
The Coast Guard and the mountain rescue service joined the search for the still missing man.
On Sunday around 7:30 p.m., police said underwater teams would search the reservoir overnight.
“The incident will take place overnight and people are reminded to stay away from the search area,” the force said.
“We are not stopping the search and are doing everything we can to locate the missing man.”