A rock embankment constructed between 1957 and 1959 has split the Great Salt Lake in Utah into two basins with very different chemical properties. The northern part of the lake, which no longer receives fresh water, has a salinity of 26 to 30 percent and appears pink due to the presence of halophilic archaea—microorganisms that thrive in highly salty environments. In contrast, the southern part of the lake, fed by three rivers—the Bear, the Weber, and the Jordan—has a much lower salinity, between 12 and 15 percent, and retains a green color because of its abundant algae. This embankment, originally a wooden structure built by the Southern Pacific Railroad in the early 1900s and later replaced with rock, physically divides the lake into two distinct ecosystems. The Union Pacific Railroad still refers to this structure as a "20-mile causeway that divides the Great Salt Lake into two." All the rivers that flow into the Great Salt Lake feed into the southern part, which supports a wide range of life, including brine shrimp, flies, and millions of migratory birds, thriving in a more balanced salinity range. The northern part, deprived of fresh water, has evolved into a unique environment. Known as Gunnison Bay, this northern arm is an open-air laboratory visible from space, where hypersaline conditions support a distinct microbial life that sometimes turns the water pink. According to the Utah Division of Wildlife Resources, the salinity in the southern arm is around 12 to 15 percent, while the northern arm ranges from 26 to 30 percent. Some 2023 measurements noted the northern salinity approaching 30 percent, nearly double that of the southern arm, which fluctuated between 7 and 15 percent. The pink color in the northern arm is primarily due to halophilic archaea, while the southern arm remains green because of its rich algal content. Two well-known organisms fall into the category of halophiles, which are organisms that require high salt concentrations to survive. From the International Space Station, these two basins appear as an unusual checkerboard pattern in the middle of the Utah desert. Images taken by astronauts and shared by NASA clearly show the distinct microbial communities from space. No other American water body offers such a striking visual contrast visible from above. The imbalance caused by the embankment eventually raised concerns among lake managers. The first response came in 1984 when the state of Utah built a 90-meter bridge at the western end of the embankment and then broke the road beneath it on August 1, 1984, allowing water from the southern arm to flow into the northern arm. This was only a temporary measure for a long-standing issue. In 2016, the U.S. Army Corps of Engineers approved the construction of a second gap, 180 feet wide, in the embankment. This new opening, completed in December 2016, aimed to manage the exchange of water between the two arms and control salinity, especially in the southern part. The temporary solution did not last. During the summer of 2022, as a severe megadrought in the southwestern United States reduced fresh water inputs, a 1.2-meter-high embankment was built within the gap under the 2016 bridge to slow the flow of salt water from the northern arm to the southern arm, which was beginning to disrupt the southern ecosystem. Even with this carefully controlled gap, the movement of salt continued in ways no one had fully predicted. Salt from the evaporation basins of the Compass Minerals company returned a significant amount of salt from the northern arm back to the southern arm. More than six decades after the railway embankment was built, it continues to shape the chemical dynamics of the entire ecosystem.