Officers were called to the reservoir shortly after 11am yesterday (Friday) after a member of the public reported seeing a body in the water.
The man was pronounced dead at the scene.
Officers have been making enquiries into the circumstances and are working to establish the man’s identity.
Detective Inspector Andrew Lockwood of Kirklees CID said: "The man’s death is not being treated as suspicious but we are appealing for help in identifying the man.
"He is described as a white male, 60-years-old, grey stubble and grey hair.
"He was found wearing black jeans, black walking boots, a red/navy jacked with a blue shirt on, he was also carrying a black rucksack.
"We would like to speak to anyone who may know the man, or saw a man matching that description around the location in recent weeks."
Anyone who witnessed anything in the area or who has any information that could help officers is asked to call West Yorkshire Police on 101 quoting log number 558 of January 11.