Progress in improving water quality and protecting human health and the environment has generally not been sufficient. Pollution of Delta waterways and persisting toxicity from legacy, regulated, and emerging contaminants continue to be present. Specifically, the extent of hazardous harmful algal blooms is increasing. Reversing these declining trends remains an important priority to support the unique and dynamic conditions in the Delta, its ecological resources, its residents and visitors, and the critical water supply services it provides.
The following Water Quality report card was developed as part of the Delta Plan Review that used the established performance measures to rate progress in implementing the Delta Plan over the past ten year (2013-2023). Read the 2024 Delta Plan Review full report to learn about additional review findings and the recommended actions that will inform Delta management priorities in next five years.
The overall performance measure score is rated “POOR” (0-25% of target met) as of 2022 based on metric:
- Proxy based on the total number of days that a specific Delta waterbody exceeds the threshold of 100,000 cells/ml cyanobacteria via a satellite-based tool. Major Delta waterbodies with a cumulative number of days when the threshold was exceeded, measured by the Satellite-based Harmful Algal Blooms Analysis Tool, are:
View more: Harmful Algal Blooms | Delta Stewardship Council (ca.gov)
The overall performance measure score is rated “POOR” (0-25% of target met) as of 2022 based on metric:
- Sediment toxicity sampled using invertebrates following standard methods approved by the USEPA and measured by the State Water Resources Control Board. Sediment toxicity increased from 39% to 50% of sites with at least one toxic sample during 2013-2022 compared to 2003-12, respectively.
View more: Measurable Toxicity | Delta Stewardship Council (ca.gov)
The overall performance measure score is rated “VERY GOOD” (76-100% of target met) as of 2023 based on metric:
- Continuous, real-time Dissolved Oxygen (DO) measurements (mg/L) measured at multiple locations throughout the Delta/Suisun Marsh. In the Delta, most of the stations that monitor DO consistently meet their daily DO objective (≥76%) during the 2018-23 period. In Suisun Marsh, stations that monitor DO also consistently meet their DO objectives (≥76%) during the 2019-23 period.
View more: Dissolved Oxygen | Delta Stewardship Council (ca.gov)
The overall performance measure score is rated “FAIR” (26-50% of target met) as of 2022 based on two metrics:
- Drinking water standards for nitrate (VERY GOOD): The 2018-2022 period shows an increase to 11% (32 out of 303 wells sampled exceeding nitrate limits) from 8% (24 out of 308 wells) in the previous 2013- 17 period. However, overall, there is about a 30% reduction compared to the baseline (2001-2013), with 15% (61 out of 402) of wells sampled exceeding nitrate limits.
- Drinking water standards for arsenic (POOR): The 2018-2022 period shows an increase to 32% (59 out of 185) of wells sampled exceeding arsenic limits, from 26% (52 out of 199) of wells in the 2013-2017 period. Compared to the baseline (2001-2013), which had 33% (89 out of 279) wells sampled, this shows minimal change.
View more: Protect Groundwater | Delta Stewardship Council (ca.gov)
The overall performance measure score is rated “VERY GOOD” (76-100% of target met) as of 2023 based on two metrics:
- Salinity compliance (VERY GOOD): Salinity compliance with objectives for agricultural and ecosystem purposes has been met at least 99 percent of the time at compliance points. Except for one station, most stations consistently met the D-1641 objectives during the 2018-23 period. In the critically dry year 2021, 25 percent of stations did not meet salinity objectives (JER, EMM, OLD, and VOL).
- Maintain Fall X2 After Wet Years (GOOD): Fall X2 was required in 2019 and 2023 due to the wet year designations. In 2019, X2 requirements for September and October were met. In 2023, the X2 requirement was met in September (~78km), but X2 was not met in October, surpassing the 80km (80.56km).
The overall performance measure score is rated “POOR” (0-25% of target met) as of 2022 based on metric:
- Delta impaired waterbodies: In the 2020-22 303(d) list, Delta waterbody contaminant combinations increased by 43% (net increase) from 2010 (baseline) and increased by 30% since the previous 2014-16 list. Pollutants included pesticides (36% of new listings), total dissolved solids (16%), nutrients (16%), other (14%), and metals (8%).
View more: Delta Water Quality | Delta Stewardship Council (ca.gov)