The original Southern-Pacific Railroad trestle (see History section) allowed for water movement and circulation throughout the lake; the filling of the causeway in 1959 all but sealed off the North Arm from the South Arm of the Great Salt Lake, creating two very different habitats. The North Arm has very little freshwater inflow, except for precipitation and a few small springs located around the lake. In fact, about 90% of the freshwater inflow to the lake occurs in the South Arm. The causeway has a small number of culverts and a narrow breach for boat passage, but water flow from the South Arm to the North Arm is restricted. As a result, the North Arm has a lower elevation compared to that of the South Arm. This restriction and variable freshwater inflow also affects mineral concentrations in the two different arms. Since 1980, salinity of the South Arm has ranged from 3-16%, while the North Arm has stayed between 16-28%.
The constant presence of Artemia in the North Arm is a mystery because conditions are so inhospitable. Brine shrimp flow from the South Arm through the breaks in the causeway to the North Arm, but little is known of their survival. Salt levels are near saturation level for sodium chloride, and lab tests have been unable to hatch cysts in North Arm water. During other tests, all adult individuals placed in North Arm water died within 48 hours.
However, populations are regularly found concentrated around D. salina algal blooms, and researchers have attempted to determine if North Arm brine shrimp have evolved capabilities to withstand high salinity and low oxygen, such as increased hemoglobin levels. In 1998, the Division of Wildlife Resources built two "limnocorrals" to test shrimp in the North Arm. The first enclosed around 7,200 liters of water and was placed in a deep portion of the bay, while the second, smaller one was in a shallow portion of the bay. Live brine shrimp captured from the corral sites were placed inside the corral, and researchers kept track of the small population to see how they fared. Very few survived, but it was not determined what caused the die-off. More research is needed to determine whether there is a self-sustaining population.