The ambulance service was told a person was in the water at The Tarn, a landscaped garden outside Mottingham station, just after 11am today (March 17).
Paramedics arrived and treated the woman before taking her to hospital.
The Metropolitan Police did not attend, describing it as a “non-crime matter”.
The lake is approximately 230 m long and between 20m and 50m wide.
A London Ambulance Service spokesperson said: “We were called today (Mon 17) at 11.03am to reports of a person in the water at The Tarn, Sidcup Road, Eltham.
“We sent resources to the scene including ambulance crews, an incident response officer and members of our hazardous area response team (HART).
“We treated a woman before taking her to hospital.”
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