Nope! You might be surprised to hear it's much closer to home, Köyceğiz Lake near Dalyan in Turkey. As you say, a beautiful, tranquil spot. I went for a 2 week holiday last year. I went across the lake on a day trip from Dalyan, swam in the water, very good medicine for the mind and soul! Dalyan is well known for it's natural mud baths and thermal hot springs on the lake shore, ancient Lycian rock tombs cut into the cliff face opposite Dalyan town (which are lit up at night to great effect), a stunningly beautiful beach set in a nature reserve to allow nesting sea turtles to breed (development is completely prohibited, hence the stunning natural beauty of the place), archaeological remains of an ancient capital sea port complete with amphitheatre, the list goes on! Highly recommended for a 'chill' holiday!