Through this web page, readers will learn about the progress of Delta Plan Performance Measures (PMs) in 2021. Some of these PMs were identified in the Delta Stewardship Council's 2021 Annual Report and discussed during the December 2021 Council meeting.

Performance Measure Spotlights


Why measure water supply reliability?

The Delta is an important water source for California, and drought is becoming routine. Monitoring the following performance metrics is a key component of conservation and drought preparedness:

  • water supply reliability,

  • water use efficiency,

  • use of alternative water sources, and

  • single and multiple dry-year reliability.

What happened in 2021?

In 2020, the California Department of Water Resources (DWR) included an example methodology for the preparation of reduced reliance on Delta elements as part of the Urban Water Management Plan Guidebook 2020. As a result, 2021 marked the first year the urban water suppliers who receive water from the Delta had a framework to support reduced reliance reporting.

By the end of 2021, 394 of approximately 440 urban water suppliers submitted their Urban Water Management Plan to the DWR.

Why is this important?

The Delta supplies water used by two-thirds of Californians, which is more than 27 million people. Delta water will be scarce during droughts, and demand will be great if water suppliers are not prepared.

Using the example methodology, water suppliers can document expected measurable reductions in reliance on the Delta and improvements in regional self-reliance, as is required for covered actions by Delta Plan Policy WR P1.

Reducing reliance on Delta water also alleviates pressures to the ecosystem and threatened and vulnerable native species.

What steps are being taken in 2022?

The DWR is reviewing the 2020 Urban Water Management Plans. Council staff anticipates updating the Urban Water Use, Alternative Water Supply, and Water Supply Reliability PMs in 2022, using data from the submitted Urban Water Management Plans.

For more details, visit the Water Supply Reliability Performance Measure PM web page.


Two invasive species of concern were reported in 2021: Ribbon Weed and Nutria

1. Ribbon Weed

What happened in 2021?

In 2021, a new non-native invasive species was found in several locations in the Delta: Ribbon Weed (Vallisneria australis). Native to Australia, Ribbon Weed grows underwater in stagnant or flowing fresh to brackish water. Often forming tall underground meadows, it has been found mainly in the northwest central Delta near Rio Vista, Liberty Island, and Sherman Lake.

Why is this significant?

When non-native invasive species establish in an ecosystem, they compete with native species. This competition is due to the lack of natural controls, such as predators. The non-native species also become nuisances by affecting other beneficial uses of the ecosystem like recreation, water supply, and flood protection.

Introductions of non-native invasive species, specifically aquatic weeds, are always a concern in the Delta because waterways are already heavily invaded. Additional non-native species may further exacerbate the already stressed Delta ecosystem by disrupting navigation, water flows and deliveries, and native ecosystem processes. New invasions further the need for management and funding to control or eradicate non-native species through additional treatments, monitoring, and research.

What steps are being taken in 2022?

The California Department of Food & Agriculture (CDFA) is proposing a B pest rating for Ribbonweed, the second-highest pest score. A pest rating indicates CDFA’s view on the statewide importance of the pest to agriculture, horticulture, forestry, and public health. Other agencies such as the California Department of Fish & Wildlife (CDFW) and the California Division of Boating & Waterways (CDBW) may initiate risk assessments, the first step to managing the weed.

2. Nutria

What happened in 2021?

The CDFW continued to manage invasive Nutria toward a goal of eradication from California. In 2021, 702 Nutria were taken from the Central Valley watershed, three of which were from the Delta. These numbers are significantly lower than those reported in 2020.

Why is this important?

Native to South America, Nutria are large semi-aquatic rodents that breed prolifically. Nutria can damage water conveyance facilities, wetland habitat, agriculture, and levees. They were first discovered in the Central Valley in 2017 and the Delta soon after.

Recent reports from the CDFW Nutria Management Team indicate that reduced take may be a hopeful sign of eradication.

What steps are being taken in 2022?

The CDFW Nutria Management Team will continue eradication efforts for the foreseeable future. Additional information about Nutria can be found on the CDFW’s Nutria web page.

For more details, visit the Terrestrial and Aquatic Invasive Species PM web page.

Graph of Nutria take
Figure 1: Bar graph of annual Nutria take.

Why measure Delta Tourism?

In 2019, the United States Congress designated the Delta as California’s first National Heritage Area, fulfilling a recommendation in the Delta Plan.

Monitoring how Delta visitors vary by season is important to businesses that support the region’s tourism.

What happened in 2021?

2021 marked the first year that seasonal visitation data was reported. The data showed that visitation differed by season. Visitation was higher in the summer and lower in the winter. [HJ1] In recent years, the Delta Protection Commission (DPC) has led an assessment of when tourists visit the Delta. In 2021, the DPC presented the findings of a survey of 857 respondents at the March 2021 and August 2021 Council meetings.

Why is this important?

The Delta is acclaimed as a world-class tourism destination that offers a diverse range of outdoor recreational opportunities such as boating, fishing, surfing, and hiking, as described on the Visit CA Delta website.

The number of Delta visitors differs by season and has an important influence on the business operations that support tourism in the region.

What steps are being taken in 2022?

The DPC is preparing a management plan for the Delta National Heritage Area. The management plan is expected to be completed and approved by early 2023. In addition, the DPC adopted the Great California Delta Trail Master Plan in early 2022, which provides a framework for local and State agencies and organizations to develop a continuous recreational corridor across the Delta.

For more details, visit the Tourism PM web page.


Pie Graph of percent of delta visitors by season
Figure 2: Percent of Delta Visitors by season


Why measure salinity?

As Pacific Ocean saltwater flows into Delta freshwater, salinity levels change in the Delta. If too much saltwater enters the Delta, it can reduce the quality of the water used for agricultural and municipal purposes and harm native species. Drought conditions exacerbate salinity conditions by reducing freshwater river flows into the Delta. Compliance stations are set up around the Delta to monitor and report salinity levels.

What happened in 2021?

In 2021, Delta salinity levels showed multiple compliance exceedances for agricultural and ecosystem objectives, which means that during that period of exceedance, the salinity levels could have negatively affected farm irrigation water, fish, and wildlife.

  • Winter: An exceedance occurred at a compliance station (S-42) in Suisun Marsh.

  • Summer: Exceedances occurred at two compliance stations: Threemile Slough (D22) and Jersey point (D15) in the western Delta.

  • Throughout the year: Exceedances occurred at a south Delta station (P12). 

Why is this significant?

Drought conditions in 2021 reduced the amount of freshwater that entered the Delta, which allowed salinity to migrate further into the Delta. This negatively affected the farmers who rely on and use Delta water because increased salinity in the water used for crops reduces crop yields and increases soil salinity.

In addition, although most compliance stations met salinity standards for ecosystem objectives, reduced freshwater flow negatively impacted native fish species by reducing ideal habitat space, which requires a certain amount of freshwater flow.

What steps are being taken in 2022?

In response to the drought, Governor Newsom declared an emergency drought proclamation and signed a $5.2 billion package of climate action bills for drought response and long-term water resilience.

For more details, visit the Delta salinity PM web page.

D1641 compliance stations
Figure 3: Map of D1641 compliance stations for Water Year 2021.

Why measure Harmful Algal Blooms (HABs)?

HABs impact water quality and public health in the Delta and are becoming increasingly frequent. The region’s unique location near major cities and agricultural hubs, combined with its low flowing and winding channels in a warm Mediterranean climate, present environmental conditions conducive to HABs.

HABs are caused by environmental factors such as:

  1. nutrient levels,
  2. water flow and chemistry,
  3. algal species composition, and
  4. temperature and sunlight exposure.

These factors may be exacerbated by human activities (such as pollution), the presence of invasive species, and reduced freshwater flows. Under climate change-driven drought conditions, the Delta may continue to experience more frequent and severe HABs.

What happened in 2021?

In 2021, HAB incidents nearly doubled compared to 2020. This dramatic year-over-year increase may be due to drought conditions and/or increased monitoring and reporting by State and local agencies.

Most HABs incidents occurred during summer in populated areas. Most were assigned cautionary advisory levels, which means that harmful algae may be present, but a few were labeled as dangerous, which means that toxins from algae in the water can harm people and animals.

Why is this significant?

When HABs occur, they can harm humans, wildlife, and domestic animals that encounter or ingest water from the affected water body. Direct human health impacts can range from minor rashes to liver and kidney harm and neurological system damage. HABs can be lethal for wildlife and pets.

What steps are being taken in 2022?

Historically, monitoring HABs in the Delta has been limited to volunteer reporting and limited response and monitoring by State and local agencies. Recently, partly due to the passing of AB-834, efforts have ramped up, and sightings, reports, and responses to HABs incidents have increased over the past couple of years. These reports are tracked by the California Cyanobacteria and HAB Network and State Water Resources Control Board HABs incident reporting tool. Local agencies (for example, East Bay Parks) may also be tracking HABs on their respective websites.

For more details, visit the HABs PM web page.


Locations of HABs in 2021
Figure 4: HABs Locations of Reported Incidences in the Delta in 2021.

Why measure flood risk reduction?

The Delta is an inherently flood-prone area comprising several low-lying and some below sea-level islands. Levees protect about 740,000 acres of land from catastrophic flooding events. Reducing flood risks to people, property, and State interests is critical to achieving the coequal goals and protecting the Delta community. The Delta Plan’s risk reduction PM reports expected annual fatalities and damages.

What happened in 2021?

Between 2007 and 2017, expected annual fatalities and property damage from flooding decreased significantly due to improvements to urban and rural levees, newer elevation data, and updated probability of flooding calculations.

In 2021, Council staff completed an effort to incorporate this new information into the Delta Levees Investment Strategy (DLIS) flood risk modeling.

Why is this important?

Better data and improved methodology demonstrate that risk to life and property from Delta levee failure is lower than 50% of previous estimates. These new results demonstrate both the value of investments made in levees over the last decade and the need to continue improving data and methods for evaluating flood risk in the Delta.

What steps are being taken in 2022?

Council staff is currently working to reinitiate the rulemaking process to amend Section 5012 and Section 5001 to implement DLIS.

For more details, visit the Flood Casualties and Damages PM web page.