The body of a baby found abandoned in a stream may have been there for up to a month, police said today.
Tests showed the infant had probably been at the bottom of the brook in Kirkham, Lancashire, for between two and four weeks.
Detectives believe the badly decomposed body is that of a full-term white girl.
The alarm was raised on Saturday afternoon when a dog walker found the body in fields off Carr Lane in a rural location about half a mile from the town centre.
The officer leading the investigation said he could not rule out foul play at this stage as the death remains unexplained but it was more likely a case of child abandonment.
Detective Superintendent Neil Esseen said: "It is vital we found out what has happened to this child and who its parents are.
"We could be dealing with a mother with emotional needs who has found herself in tragic circumstances. There must be concern for the physical and emotional health of this woman.
"My message to her or anyone who knows her is that we are not here to judge you but to try and help, so please get in touch with us.
"This is one of the cases where the public input is vital.
"We believe from pathological tests that the child has been outside in the open from between two and four weeks."
There is no direct vehicular access to the stream but Mr Esseen said that did not necessarily imply that the person who left the child was local as he emphasised the appeal was nationwide.
The baby was wearing a brown fleece jumper with a motif of a cartoon dog from George at Asda, and two muddied towels, one green and one with a Union flag pattern, in a Blackpool Borough Council bin bag were found about 20m upstream.
Anyone with information should call Lancashire Police on 08451 253545 or they can contact Crimestoppers anonymously on 0800 555 111.