California’s Drought Response Will Worsen Harmful Algae

HABs in the Delta 2021

Credit: photo courtesy of Michael Greggans

Climate change has created new “seasons” that challenge communities across the nation. California now has a “fire season,” and sadly, we are embarking on harmful algal bloom (HAB) season again. NRDC has updated its national map of state-reported freshwater HABs, which tracks the HABs reported by states from 2008-2020 and shows that these toxic outbreaks are increasing across the country, making our rivers, lakes, and beaches unsafe for swimming, boating, and drinking. Between 2008 and 2020, over 44,000 HAB events were recorded across 38 states. This is bad news for the health of our waterways and public health. The World Health Organization calls the bacteria that make algal blooms harmful (cyanobacteria) “among the most hazardous substances widely found in waterbodies.” Some scientists even suspect a link between cyanobacteria and amyotrophic lateral sclerosis, the fatal neurological disease also known as Lou Gehrig’s disease.


California has experienced some of the worst HAB outbreaks in the country. Within the past five years, the number of HAB events observed in California has increased more than 464 percent, from 56 in 2016 to 316 in 2020. In 2020 alone, California experienced a 60 percent increase in reported HABs from 2019. From the Klamath River and Clear Lake in northern California, to Lake Isabella  and Lake Elsinore in southern California, HAB outbreaks have occurred in recent years throughout the State. California’s Bay-Delta estuary—and the San Joaquin River around Stockton—have been particularly hard hit by HABs due primarily to low flows caused by excessive water diversions upstream of the Delta. And this year is threatening to bring one of the worst HAB outbreaks ever around Stockton, thanks in part to California’s own Department of Water Resources (DWR).

DWR recently asked the State Water Resources Control Board (SWRCB) to exempt it from meeting water quality standards in the San Francisco Bay-Delta this summer. DWR’s requested exemptions would allow it to reduce freshwater flows in the Delta below the levels required in outdated 1995 water quality standards, which are already widely recognized as insufficiently protective. What this means for the people living in the Delta, including Stockton, is that water quality will deteriorate and harmful algal blooms will proliferate.  

The State’s own water experts have confirmed that when freshwater outflow from the Delta is reduced—which translates into a measurement known as “X2” when saltwater and freshwater meet in the estuary moving upstream—HABs worsen and people’s health is imperiled. In a peer reviewed paper published in 2020, DWR senior scientist Dr. Peggy Lehman concluded that Delta outflow, characterized by the X2 index, is the most important variable in increasing HAB occurrence, noting that "relatively small changes in the location of the X2 index may be important. A shift of the X2 index by only 3 km was associated with a factor of 3 increase in the percent abundance of subsurface Microcystis cells...." Lehman et al 2020. Dr. Lehman has further explained that “[w]hen X2 is 85 kilometers or more, there are a lot of blooms in the system.” Noting the large number of HAB outbreaks in the Delta in 2020 (shown below), she urged that “given what we had last year, in 2020, we need to focus on safety. …It is dangerous for people to be in the Delta. And this is a huge recreational area and huge fishing area, so it's a problem.” 


Similarly, the state-appointed Delta Watermaster explained that in 2020:

“[I]f you happened to be in downtown Stockton where the Delta comes into downtown past the port, the algae was thick and smelly. There were multiple reports of people whose pets got in contact with it and either got very sick or died. If you were down there, you would have noticed that along those waterways were homeless encampments. And people who were using that Delta water to wash sometimes, and even though they boiled water, they were using it to cook, and they were getting sick. The most easily seen and understood disadvantaged communities are the people who are forced to camp along these waterways.

It is in the city of Stockton, but it is also in other areas in the southern Delta…. So what can we do? …[H]onestly, the biggest thing you can do to improve the southern Delta is to open up the channels and to drive more water through those channels.

Despite these warnings, DWR proposes to do the opposite and reduce freshwater flows through the Delta this year, worsening HAB outbreaks for Stockton and other at-risk communities. Even more alarming for public safety, DWR is trying to hide the harmful impacts of its proposal by mischaracterizing the science and falsely downplaying the HAB threats. DWR’s petition to the SWRCB states that “[t]he extent to which the TUCP’s changed operations from baseline conditions would affect harmful algal blooms is uncertain but likely small given that water temperature is the main driver of bloom intensity (Lehman et al. 2020a).” But the study that DWR cites (Lehman et al. 2020a) states no such thing, and instead demonstrates that reduced outflow, characterized by the X2 index, is likely to increase the proliferation of harmful algal blooms in the Delta this year.

While DWR’s own scientists confirm that its proposed action will make HAB outbreaks worse in the Delta this year, threatening public health and safety, DWR continues to allocate over 800,000 acre-feet of Delta water to its contractors this year. Unless and until DWR reduces those allocations to zero, it should not be permitted to put the health and safety of the people of Stockton and the Delta at risk by worsening HAB outbreaks. DWR created the mess it finds itself in this year by failing to appropriately plan for drought after the disaster of 2014 and 2015, calling it too "speculative" to do so. While the State Senate has proposed some funding in its drought package for monitoring and reducing HAB outbreaks during the drought—which will help—money can’t substitute for the water needed to keep HABs at bay.

To check out whether states have reported HABs near you, click here.

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