Despite falling river flows and lower reservoir releases, the US Bureau of Reclamation and the California Department of Water Resources maintained Delta outflows and the prescribed fall salinity in the Delta (X2 located at Chipps Island, River Kilometer 74) in the last half of August, September and October 2019. They did this by sharply reducing Delta exports (Figures 1 and 2). These actions helped to maintain low salinity habitat in (and flow through) Montezuma Slough in Suisun Marsh (Figure 3).

High Delta outflow and reduced Delta exports in September and October are good for all Delta native fishes. These conditions protect wild juvenile winter run salmon that began migrating downstream into the Delta (Figure 4). Delta smelt and longfin smelt remained in the Bay, west of the Delta.

Fall X2 was a provision of the 2008 and 2009 Biological Opinions for the Long-Term Operations of the Central Valley Project and the State Water Project. It applied only in Wet and Above Normal water years. New Biological Opinions released in October 2019 have moved the initial compliance point for the Fall X2 requirement upstream to River Kilometer 80, reducing low salinity habitat by pushing it further up into the Delta. ¹

Figure 1. Delta Exports (TRP and HRO) and Outflow (DTO), and Lower Sacramento River flow at Wilkins Slough (WLK), Verona (VON), and Freeport (FPT).

Figure 2. Salinity (EC) at Mallard Island (km 74), the Fall X2 prescribed location under 2008 Delta smelt biological opinion. X2 is approximately 3800 EC.

Figure 3. Salinity (EC) in Montezuma Slough in late summer and fall 2019.

Figure 4. Winter run catch in juvenile salmon monitoring in summer-fall 2019. Sacramento beach seine stations are in the north Delta.