Most water demand is currently satisfied through seawater desalination plants. The most common electrolyte is water, ranging from freshwater to seawater. The density of seawater also changes with salinity. Sea salt is salt that is produced by the evaporation of seawater. Some magnesium chloride is made from solar evaporation of seawater. These are seawater (or at least brackish water) and light sufficient to support photosynthesis. Perth began operating a reverse osmosis seawater desalination plant in 2006. The most abundant solid dissolved in seawater is sodium chloride. They later found probable iodine deficiency disorders in a population reliant on desalinated seawater. The formation of sea ice produces ice with little salt, much lower than in seawater. Shandong also produces bromine from underground wells and salt from seawater. The temperature of maximum density of seawater decreases as its salt content increases. The only angiosperms capable of growing completely submerged in seawater are the seagrasses. Porphyra is a coldwater seaweed that grows in cold, shallow seawater. Tests were conducted on samples of cable submerged in seawater.