That’s salt crusted on the top of the very shallow evaporation pool of sea water.
The salt is then scraped off witha long trowel-like tool (you can see the piles of salt better in the previous pic). It’s then ground and then sent to salt factories where they are iodized for human consumption.
(Last one from Marakkanam – LOL!!)
Sigma 10-20 @ 12mm
f/11 @ 1/45 ISO 100
HiTech Graduated ND filter (3 stop)