The clothed body was found in a bag which was first spotted on Wednesday and reported to police at 09:00 BST yesterday.
Police say that the dead woman is white and is believed to be in her 20s or 30s. They have not yet identified her.
A post-mortem is due later today when it is hoped that more information about the cause of death will be revealed.
Detectives have questioned a man from south London in relation to the death and bailed him to return to a police station next month.
"We believe the bag was seen by members of the public in the water on April 18th, but was reported to police on April 19th," a Metropolitan police spokeswoman said.
"It is thought the body had been in the water a short time."
A murder inquiry has been launched and the post-mortem is due to take place at Greenwich mortuary this afternoon.
Click here to run an energy price comparison, and see if you could be paying less for your gas and electricity.