Police were called to Shorey Bank park in Darwen at around 8.40am yesterday (Wednesday, March 6) after a body was spotted in a shallow brook.
Police divers entered the brook, which forms a narrow stretch of the River Darwen, and recovered the body from the water.
A post mortem examination to establish the cause of her death took place yesterday evening, but a specific cause of death could not be found.
But detectives said they are not treating the death as suspicious.
Further tests will take place to try and establish how the woman died and how her body entered the water.
"We do not believe her death was suspicious and for now our priority is identifying who the woman is and tracing her family."
If you have any information that you feel can help the investigation, please call 101 quoting incident reference 256 of March 6.