A woman drowned after going into the river at Moulton Marsh Nature Reserve to rescue her dog, police have confirmed.
Reports suggest she went into the River Welland in a bid to rescue her pet after it got into difficulty.
A huge emergency services operation was launched at 10.15am on Friday when police got the initial call about the incident.
Three helicopters, including the NPAS police helicopter, several boats, and a police drone were all involved in the search, with the Coastguard Agency, East Midlands Ambulance Service, and Lincolnshire Fire and Rescue Service all providing support for the police.
But after an intensive search of more than three hours, the body of a 35-year-old local woman was discovered.
Lincolnshire Police's inspector for the South Holland area Gary Boxall said on Friday: "At 10.15am we were called to the nature reserve at Moulton Marsh to a report of a lady having entered the River Welland.
"For several hours we worked with Lincolnshire Fire and Rescue, East Midlands Ambulance Service and Her Majesty’s Coastguard to try to locate this lady.
"Air support from three helicopters, several boats and our own drone were unfortunately unable to locate the lady. I am very sad to report that at 13.35pm we found the body of a 35-year-old local woman and we have informed her next of kin of her death.
"We are not treating the incident as suspicious."