The victim, identified in local media as a 45-year-old English woman, died when the vessel she was travelling in collided with a water taxi in front of horrified holidaymakers off the coast of Marmaris, Mugla.
Emergency services responded to the incident, which took place in view of the five-star Elegance hotel at around 1.30pm local time on Thursday, but were unable to save her.
The woman’s husband was taken to hospital and placed in an intensive care ward, according local media, which published footage of the boats colliding and pictures of the damaged speedboat after it was brought to shore.
It is unclear at this stage what caused the collision and police have launched an investigation.
Four people travelling in the water taxi suffered less serious injuries and were taken to Ahu hospital in the popular holiday resort.
A 44-year-old London woman on holiday in Marmaris told The Sun: “It was an awful crash and a lot of the people who saw it were wandering around in shock.
“Some of the injured were in a terrible state and the dead lady was brought ashore in a body bag – she clearly had no chance.
“The sea was a bit chaotic with so many speedboats and para-sailing boats roaring around but no one ever expected this.”
A spokesperson for the Foreign, Commonwealth and Development Office said: “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.”
Marmaris is a Mediterranean resort town along Turkey’s southwest coast and is popular with British tourists.
It is known for its lively nightlife and home to open-air clubs and music venues.