Turkey is a predominantly Muslim country and the dress may be more conservative than some other parts of the world - for both men and women. While you won't likely see the locals in tube tops, gangsta pants or short shorts, there is no requirement for anyone to be fully covered. In fact, it is uncommon to see women wearing full burqa in Fethiye, although colourful headscarves are quite popular.
Most people living in Turkey’s tourist-centers are open-minded and welcome guests to their country regardless of clothing choices.
The only exception to the “not fully covered" requirement is when visiting mosques, where women are required to cover their hair, arms and legs - to avoid distracting the men from their prayers. Most mosques provide loaner scarves and long, slip-on skirts to women who are not sufficiently covered.
During land excursions, we suggest that our female guests carry a light scarf (or two) to allow for the option of covering head and arms if feeling uncomfortable or in situations warranting conservative attire. (Beautiful scarves can be purchased for only a few Turkish Lira throughout in the country.)
Please note that the same standards do not apply onboard the boat. You are welcome to wear whatever you like, exposing as much (or as little) skin as you are comfortable with. Just don't forget to apply sunscreen!