The woman was killed at about 1.30pm on Thursday off the coast of Marmaris in southern Turkey, when the speedboat she was in collided with a water taxi, according to local reports.
Local media also said the woman’s husband was critically injured, but was in a stable condition in hospital on Thursday night.
Four people riding in the water taxi were also reportedly hurt. The Foreign Office said three Britons were taken to hospital following the incident.
Footage from the Turkish Demiroren News Agency showed two boats colliding close to the shore. Onlookers could then be seen rushing to help.
A Foreign Office spokesperson added: “We are providing consular assistance after the death of a British woman and hospitalisation of three British nationals in Turkey, and are in contact with the local authorities.”