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.
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.”