Whatever the white beaches at Lake Salda are, they are not sand. They are hydromagnesite, a rock still being made in the shallows of this closed basin in Burdur province, southwestern Türkiye. Cyanobacteria and algae pull magnesium out of the water and lay it down as lumpy mounds; the waves grind those mounds into pale grains that crunch under your feet rather than slip. The magnesium comes off the hills around it, where serpentinite weathers into water that ends up alkaline and carrying the metal. Very few places on Earth are still making rock this way. That is why NASA sent scientists to wade here before the Perseverance rover landed in 2021: carbonate minerals ring the old shoreline of Jezero Crater on Mars, and these are the closest known match. The hard question is which textures would prove ancient life rather than plain chemistry, and Salda is where that reference comes from.
Out from the marked beaches the water over the white shelf is clear enough that the floor seems to hold the light. You wade a long way before it deepens, and further out the pale shelf gives way to deep green. The colour sorts itself by depth: milk in the shallows, turquoise over the shelf, bottle-green where the bottom drops away. Only July and August are warm enough for swimming. People walked over the mounds for years and smeared the white paste on their faces, so the islands and the water off them are closed now, and you look from behind a wooden barrier. From the black pines on the slopes above, you get the whole arrangement: white rim, shallow shelf, dark middle, the line between them startlingly sharp. Nothing flows into this basin but rain, snowmelt and springs, and nothing drains out, so the lake has come down three or four metres in two decades. The mounds only grow in shallow water, which means a dry summer, or one more pump sunk into this ground, is read straight off the width of the white shore.