Missing man's body found in Sydney river

A man's body has been found in the Hawkesbury River, north of Sydney.

Police and SES workers found the man's body north of the Windsor Bridge, just before the Windsor boat ramp, on Sunday.

They have not formally identified the body but it is believed to be that of a 21-year-old Quakers Hill man who got into difficulties and disappeared while swimming in the river on Friday afternoon.

His friends told police they tried to help him after he began struggling while swimming at Windsor Beach, but they weren't able to reach him and he disappeared underwater.