The complex chemistry of Great Salt Lake shapes every aspect of its ecosystem, from microbial communities to bird populations. As a critical stopover on the Pacific Flyway, the Lake's health has far-reaching impacts beyond its meander line. Understanding and effectively managing salinity levels has become increasingly important as Lake levels continue to fluctuate. Adaptive management tools, like the causeway breach and its berm, play a vital role in this effort, offering flexible responses to changing conditions at Great Salt Lake. As we see how quick and effective these tools are at altering the Lake's chemistry, it is imperative that we learn to use them in ways that protect the health of Great Salt Lake - the entire Lake - in perpetuity.
Historical Context
The story of the causeway in Great Salt Lake dates back to the early 1900s, when the Southern Pacific Railroad constructed the Lucin Cutoff to improve transportation efficiency across Utah. Originally a wooden trestle, the crossing was replaced in the 1950s by a rock-filled causeway, physically splitting Great Salt Lake into two distinct environments. With little freshwater inflow, the North Arm (Gunnison Bay) became hypersaline, supporting unique microbial life that at times colors the water pink. At present Lake levels, the North Arm has reached salinity concentrations that exceed thresholds for the diverse ecosystem that once thrived there. In contrast, the South Arm, fed by the Bear, Weber, and Jordan Rivers, fosters a broader array of species, including Brine Shrimp, Brine Flies, and millions of migratory birds, all of which depend on a balanced salinity range of approximately 120-160 g/L (12-16%). The majority of Great Salt Lake’s functional ecosystem relies on the South Arm and associated wetlands.
Hypersaline waters in the Lake's North Arm. Photo: Doug Tolman
In 1984, a 290-ft breach was built near the western edge of the causeway to improve flows between the North and South Arms. As Lake levels dropped below 4,195 in the 2010’s, water stopped flowing through this breach, and the only water exchange between the two arms was through two small culverts on the east side of the causeway. Structural stability concerns led Union Pacific Railroad (UPRR) to permanently close these culverts in 2012, completely bifurcating the Lake once again. To address the need for hydrological connectivity, the U.S. Army Corps of Engineers (USACE) approved the construction of a second, 180-foot breach in the causeway in 2016. Colloquially known as “the breach”, this structure aimed to re-establish balance between the North and South Arms. After six years of water exchange between the Arms, it was observed that while water flowed from the South Arm into the North, dense brine from the North was cycling back underneath, increasing the salt load in Gilbert Bay. Additional salt was, and still is also entering the South Arm through groundwater, though it is unknown how much. Further, salt that is flushed out of Compass Minerals’ evaporation ponds returns a significant amount of salt from the North Arm back into the South Arm. By the time the Lake reached historically low levels in 2022, this salt load had elevated salinity to over 180 g/L (18%), an ecological “cliff” that could have severe repercussions if not quickly addressed.
An Ecological Cliff
The risks of this ecological cliff are highlighted in an emergency petition we filed in October 2022 requesting that the waters of Gilbert Bay be classified as impaired. Our petition, submitted while salinity levels were in excess of 180 g/L (18%), referenced a letter we received from Dr. Bonnie Baxter, of Great Salt Lake Institute at Westminster University. Dr. Baxter’s letter summarized research emphasizing that sustained high salinity levels would lead to a collapse in the Lake’s ecosystem. Findings by Dr. Baxter and others, including modeling by Dr. Gary Belovsky for the Great Salt Lake Ecosystem Program (GSLEP) demonstrate that salinity levels in excess of 180 g/L (18%) disrupt the foundational algae and cyanobacteria essential for the survival of Brine Shrimp and Brine Flies. These keystone species form the base of the Lake’s food web, supporting millions of migratory birds; disruption in this cycle would inevitably lead to mass die-offs throughout the Great Salt Lake ecosystem. In late 2022, signs of this collapse - including smaller Brine Fly larvae, declining Brine Shrimp populations, and emaciated Eared Grebes - were already observed. These declines likely would have continued without the significant precipitation received in the 2022/2023 water year.
For context, Utah Division of Water Quality (DWQ) recognizes that the waters of Gilbert Bay are “protected for frequent primary and secondary contact recreation, waterfowl, shore birds and other water-oriented wildlife including their necessary food chain.” Utah Admin. Code R317-2-6.5(a). This petition to recategorize Gilbert Bay as impaired came in the light of a request by US Magnesium to extend their canals further into Gilbert Bay, which would have lowered Lake levels and increased salinity even further. The recategorization would have acknowledged the impairment of Gilbert Bay’s beneficial uses, requiring DWQ to take action.
In Spring 2024, DWQ requested public comment on an Integrated Report that again categorized Gilbert Bay as a Category 2 (unimpaired) waterbody. This report was based on a two-year period covering 2022 and 2023; much of this time salinity exceeded the 180 g/L (18%) threshold that the Great Salt Lake Advisory Council recognizes as impairing beneficial uses. Though we appreciate the ongoing work done by DWQ, we disagreed with their decision and submitted a public comment again asking them to recategorize Gilbert Bay as impaired.
House Bill 453, passed in Spring 2024, introduced new salinity management requirements for Great Salt Lake. This law directed the Utah Division of Forestry, Fire, and State Lands (FFSL) to establish an emergency trigger based on best practices as recommended by the Salinity Advisory Council (SAC). Applying to salinity concentrations below 90 g/L or exceeding 150 g/L, this trigger gives FFSL authority to curtail or withdraw mineral leases, require operators to implement non-evaporative extraction methods, and to modify the adaptive management berm in the railroad causeway.
Developing Adaptive Tools to Manage Salinity
To curb the risks posed by increased salinity, the state added a simple rock berm at the bottom of the breach at 4,187’ (ASL) in early 2022 to block the dense brine layer (DBL) from returning to the South Arm, colloquially known as "the berm". Raised to 4,192’ in 2023, ASL the the berm has since naturally eroded into a V-shape, lowering the bottom to approximately 4,189’ by Fall 2024. FFSL is currently searching for a more sustainable, mechanical alternative to the rock berm that can be easily adjusted to meet changing conditions.
Contractors with the Utah Division of Water Resources raising the berm in 2023. Photo: Utah FFSL
Water flowing over the berm in Fall 2024, Lake elevation 4193' ASL. Photo: Doug Tolman
Along with salinity requirements, House Bill 453, signed into law in Spring 2024, mandates that the two arms be managed within two feet of one another, aiming to prevent the six-foot or greater discrepancies observed in the past. This policy change coincided with historically wet winters in 2023 and 2024, which introduced a massive volume of freshwater into the South Arm. As water flowed northward through the breach, much of the South Arm’s salt mass traveled with it, an unanticipated result of the flow equalization process. This caused a significant shift in the Lake’s salinity profile: as of November 2024, the South Arm is now within its ideal salinity range, yet the relationship between water level and salinity concentration has changed. Previously, the South Arm would reach the critical 18% salinity cliff around 4,190’ ASL, but now, due to this northward salt migration, that point has effectively shifted three feet lower to 4,187’.
Updated Salinity Curve presented by the Great Salt Lake Brine Shrimp Cooperative in the October 2024 Salinity Advisory Committee Meeting
The adjusted salinity curve shows just how quick and effective the berm is as an adaptive management tool, but also presents new challenges. With the cliff face of 18% salinity now effectively at 4,187’ ASL, there is a new buffer that provides flexibility against reaching the threshold at lower water levels. However, this shift complicates efforts to return to the designated healthy range (4,198 - 4,205’) as outlined in the Great Salt Lake Commissioner’s Strategic Plan. Should we reach that range without addressing this shifted salinity curve, the South Arm would risk becoming too fresh, even under 8 g/L (8%), which could destabilize the Brine Shrimp, Brine Fly, and microbialite populations that depend on optimal salinity. While this shift may temporarily protect the South Arm ecosystem from hypersalinity, other critical concerns remain. Microbialites, navigation, and dust storm events are all impacted by low Lake levels, continuing to impact the health of the Lake and surrounding communities regardless of salinity levels.
Looking Forward
FRIENDS acknowledges the berm as an important adaptive management tool and applauds the work of the Salinity Advisory Committee, FFSL, and other partners to ensure the Lake's chemistry is balanced. As we see how quick and effective the berm is at altering salinity, it is imperative that we learn how to use this and future adaptive management tools thoughtfully. The distribution of both salt and water across Great Salt Lake's various arms and bays must be managed with the preservation of the entire Lake in mind. Success will require not only precise salinity management but also proactive efforts to ensure stable freshwater inflows, supported by continued collaboration among agencies, industries, and communities committed to protecting Great Salt Lake.