The woman, aged in her 20s, got into difficulties in the water near Old North Pier, near Sunderland Yacht Club, in Roker shortly, before 4am on Sunday.
Sunderland RNLI’s D class boat was launched with volunteers rescuing her a short time later.
Coastguard and police officers met her on the shore.
The woman, who is suspected to have been drinking alcohol, was pulled from the sea by RNLI crews and handed over to paramedics for further treatment.
She was then arrested by police, before being questioned on suspicion of causing a public nuisance.
An RNLI spokesman said: “While it is unclear how this female ended up in the sea; she is extremely lucky to survive.
“We strongly recommend not going into the sea after drinking alcohol as they simply do not mix.”
A spokeswoman for Northumbria Police said: “At 340am police were informed a woman was in the water just off Marine Walk, Sunderland. “The woman was brought back to safety by the RNLI.
“The woman, in her 20s, was arrested on suspicion of causing a public nuisance.”
Water Safety Map would like to ask that you take care when near water and especially when you could be under the influence.