The man, believed to be aged in his 70s remains in a critical condition in hospital after being pulled from a canal in Stalybridge on Friday
He had been pulled out of the Huddersfield Canal, close to the Tesco supermarket, by passers-by around 6.00pm
Detective Inspector Phil Key said: “An elderly man remains in a life-threatening condition in hospital and our thoughts are with him as he continues his recovery.
“While there is currently no suggestion of third party involvement, we are treating this incident as unexplained, and we are determined to find out how he came to be in the water.
“Were you in the area at the time? Did you see or hear anything that seemed out of place?
“If you have any information that can assist our enquiries then please get in touch as soon as possible.”