Police and paramedics attended Hartlepool Marina at around 4am after concern for the safety of a woman.
She was rescued by emergency services and treated by paramedics at the scene before being taken to North Tees Hospital.
A Cleveland Police spokeswoman confirmed officers were involved in the incident.
She said: “Police attended a report of a concern for safety of a woman at Hartlepool Marina around 4am this morning, Sunday, July, 25. Officers attended the scene and the woman was taken to hospital by ambulance service colleagues.”
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A spokesperson for the North East Ambulance Service said: “We got a call at 4.04 am this morning for report of a person in the water.
“A paramedic crew attended and treated a woman who had been rescued by emergency services.
“They took her to North Tees Hospital.”