Despite a relatively cool May, the Delta is very warm under conditions of low river and Delta flows and low outflow to the Bay that the State Water Board has allowed by weakening flow standards. As in 2014, water temperatures in early June approach the lethal level for Delta Smelt of 73°F¹ (Figure 1). The water temperatures now (and in 2014) are several degrees higher than in 2012, the last year in which the normal dry year flow standards were followed.

The first heat wave of summer, with air temperatures forecasted from 95-100°F, is predicted to begin early next week. Water temperatures in the entire Delta are expected to reach the lethal level of 73°F or higher. The water temperature may be further degraded in the north and central Delta by the opening of the Delta Cross Channel in combination with the new False River Barrier (FAL location on map).

Delta Smelt are presently confined primarily to the Sacramento Deep Water Ship Channel, where water temperatures are already near lethal levels (Figures 2 and 3). Reclamation scientists theorize that smelt can survive in deeper, cooler waters. I challenge Reclamation to prove this theory by monitoring water temperature and taking dissolved oxygen profiles throughout the Sacramento Deep Water Ship Channel all summer.

Figure 1. Water temperature in the Delta in first week of June 2015.
Based on water temperatures recorded at CDEC stations (blue dots).

Figure 2. Water temperature in the Sacramento Deep Water Ship Channel,
May 28 – June 6, 2015.

Figure 3. Distribution of Delta Smelt catch in 20-mm Smelt Survey May 2015.
All but three young smelt were captured in the Sacramento Deep Water Ship
Channel . Water temperature at the time of the net deployment in the
Channel was 65°F (at surface).