A senior detective said the body found in a well outside a home in Surrey "presents a number of logistical challenges".
Detective Chief Inspector Cliff Lyons said:
The well is two feet in diameter, it is seven feet deep to the water line, and the water is approximately four feet deep.
We need a police marine diving team, with breathing apparatus, and we need to recover the body intact to preserve forensic evidence.
The process of recovery is likely to take some time.
Although it is not possible to ascertain the gender of the body with accuracy, "judging by the size, it is most likely to be an adult, not a child", he said, adding, "The person is white."
More top news
Turning colder and brighter towards the end of the the week.
Detectives have launched a murder investigation after a man was fatally stabbed in Kensington.
Stars appeared in black as they called for an end to harrassment at the UK's film awards night.