The northern part of the Great Salt Lake is pink due to the algae that can survive in the hyper-saline environment.
Great Salt Lake
The Great Salt Lake is saltier than the oceans. This trait gives it scientific properties that can be experienced directly. The high levels of salt give the lake water solution a high density. Because of this high density, it is very easy to float. The density of the Great Salt Lake is greater than the density of your body, while a freshwater lake has a density lower than that of your body. Comparing the ease of floating here with the ease of floating at a freshwater lake is a very concrete way of experiencing the effects of density.
Lakes become salty because there are minerals in water, even in freshwater. In freshwater, these minerals are just very diluted. But when freshwater flows into a lake, a certain number of minerals enter the lake too. What happens to these minerals, and to the water itself, is what determines if a lake becomes salty or not.
In all lakes, various things can happen to the water that enters the lake. Water can leave by means of a stream that exits the lake and flows towards an ocean or a lower lake basin, it can absorb into the ground to become groundwater, or it can evaporate into the air. If a lake has an exit stream, it is common for the amount of water entering the lake to equal the amount of water exiting the lake. There will always be a certain amount of evaporation and absorption into the ground from any body of water, but the amount is usually insignificant in this scenario. So, in this case, the concentration of minerals flowing into the lake is about the same as the concentration flowing out, which means the concentration of minerals in the lake itself is about the same. If a lake does not have an exit stream, as is the case with the Great Salt Lake, the only way for water to exit is by evaporation and absorption into the ground. For the Salt Lake, the main path is evaportaion.
During evaporation, the water molecules leave the lake but the minerals are left behind. That means that the amount of minerals per unit of water in the lake is increasing. Increased minerals per unit of water means the water is becoming more concentrated with minerals which means it is getting saltier and more dense. Unless fresh water enters the lake at a rate faster than water leaves the lake by evaporation, the lake will become saltier and saltier. This is the scenario that has made the Great Salt Lake as salty as it is today.
The saltiness of the lake also makes it inhospitable to many living things. For all organisms, there is a certain amount of water that cells need inside them to survive. If a cell doesn't have enough water, the cell will not function properly. This state is called dehydration. The types of organisms that can survive in the highly saline environment of the lake are unique. Somehow these organisms must counteract the effects of osmosis to keep themselves from getting dehydrated. Osmosis is basically a force that tries to get the concentration of minerals in water on two sides of a barrier to be the same. The barrier that concerns a living thing is its cell membrane, which separates the inside of the cell from the outside.
If the concentration of minerals outside of the cell is about the same as on the inside, the force, or pressure, from osmosis is very small and everything stays fine inside the cell. If the concentration of minerals outside the cell is much lower than inside, the pressure of osmosis will force water into the cell, in an attempt to dilute the concentration of minerals inside the cell to equal the concentration on the outside. If the pressure is high enough, the cell can actually burst, which, of course, will kill the cell.
If the concentration of minerals outside a cell is much greater than inside the cell, osmosis works in the opposite direction. Water will be drawn out of the less-concentrated cell interior in an attempt to balance things, which means there may not be enough water inside the cell for crucial chemical reactions to occur. This is the scenario with which organisms must deal in the Great Salt Lake. Brine fly larvae, brine shrimps and all the microorganisms in the lake must have some mechanism for keeping water in their cells. Or they have to be able to function with less water in their cells. In either case, the organisms that can live in the lake have some kind of adaptation to the saltiness that most living things don't have.
No fish species have adaptations that allow them to survive in the lake. Fish are occasionally present in the lake but only when freshwater streams are flowing into it. Where the fish live, it is not very salty at all. But some animals, such as brine flies (Ephydra spp.) and tiny animals called brine shrimp (Artemia franciscana), have adapted to the actual lake environment. There are also various types of algae that have adapted to the salty environment. Because of the adaptations of brine shrimp and brine flies, many birds can be found at the lake. The flies and shrimp are the birds' source of food.
Because of a railroad causeway that runs across the lake from east to west, almost completely separating the the northern arm from the rest of the lake, there is very limited mixing of water between the northern arm and the rest of the lake. Since the northern arm, known as Gunnison Bay, has no rivers flowing into it, and the only water that enters it directly is infrequent rainwater, there is very little fresh water to dilute the saltiness in the northern arm. The Great Salt Lake in general is around four times as salty as the ocean but the northern arm is around eight times as salty! Gunnison Bay is so salty that even the brine flies, brine shrimp and most algae cannot live there.
But even in this extreme environment, there are a few organisms that exist. Microorganisms that live in this part of the lake are called halophiles, a type of extremophile that thrives in very salty environments. They are in the domain of life know as Archaea. Archaea, in general, are extremophiles of various kinds and we saw other kinds in Yellowstone. Archaea that are thermophiles thrive in very hot environments. Methanophiles love high levels of methane. An acidophile could be found in one of the hot springs with a very low pH. Halococcus and Halobacterium species are two types of organisms that thrive in the saltiness of Gunnison Bay. It just so happens that these halophiles have purplish pigments in them. Because they do so well in the bay, and exist in such high concentrations there, these purplish pigments make the water look pink! These organisms are not known to be harmful to humans. I wouldn't go drinking the water from Gunnison Bay, if for no other reason than it is salt water, but it is safe to swim in the water with the archaea to experience the bouyancy effects discussed earlier. It is quite a surreal experience to bob around like a cork in a sea of pink water!
Pink waters of the northern arm of the lake, tinted by archaea and algae.