Freshwater Flows, Reduced Diversions Help Abate Toxic Algae

Photo credit Erik Stine

A dog toy was lobbed into the Sacramento River and Lilly, a three-year old Labrador retriever, leaped into the water in pursuit. It was a sunny July weekend in northern California and Lilly was cruising the river with her owners on their 20-foot Grady White. There were no indications anything was amiss. No signs at the dock or along the river’s edge warning that conditions were unusual, let alone dangerous. But that night at home, Lilly was lethargic and didn’t have an appetite. Her owners monitored her for a couple hours and when her state didn’t improve they took her to the emergency vet. At the vet, she began whimpering in pain and vomited several times. The vet diagnosed that something in the river made her sick, but a lot of details were unknown. It was only after an algal bloom was detected in the river a couple days later that answers would start appearing.

Stories like this are sadly common. Harmful algal blooms (HABs) are a growing public health and environmental threat in every U.S. state. More than just ugly, smelly scum, HABs can produce toxins that endanger people, pets, and livestock that come into contact with them. In warm, summer months with little rain, freshwater bodies are susceptible to HABs, particularly ones that are depleted to meet human needs, such as for irrigation, drinking, bathing, and industrial cooling.

Many rivers in California are flowing at less than half of their natural volume (the amount of water that would remain if no water was taken out) because water is diverted primarily for use by farms and cities. Water from the Sacramento-San Joaquin Delta (the Delta)the largest estuary on the West Coastprovides drinking water for 25 million Californians and it’s the chief source of water for Central Valley’s huge agricultural industry. Millions of acre-feet of water are exported each year from the Delta (enough to inundate an area larger than New Jersey in one foot of water), leaving the Sacramento River and its tributaries with a paltry percentage of their natural flow.

When water is diverted from rivers, the remaining water moves more slowly and warms more easily. Algae and bacteria thrive in warm, stagnant water and are more likely to grow in excess, increasing the chances of a HAB event. These same rivers that are used as a water source are often also used for recreation. A HAB can be a devastating surprise to people who use rivers or reservoirs to kayak or sport fish. That’s why it’s critically important for state agencies to monitor for HABs and alert the public in a timely, efficient manner to all HAB occurrences and their risks.

It’s not just the Delta that suffers from overdrawn rivers. Due to water removal and man-made infrastructure, like dams, rivers are flowing at lower and lower volumes across California and the Western U.S.a problem exacerbated by climate change. According to California’s Fourth Climate Change Assessment, the water supply from snowpack in the state is expected to decline by two-thirds within 80 years, which means even less water flowing into rivers. As the climate warms and carbon dioxide levels rise, cyanobacteria, the organism responsible for most freshwater HABs in the U.S., have a competitive advantage over algae that aren’t known to form HABs. 

To restore rivers and improve the health of aquatic habitat, NRDC advocates for increased flows through the Delta and litigates to ensure water operations comply with environmental laws. Our work is centered on keeping rivers and lakes healthy while providing adequate water supplies for growing populations and economies. We’re also advocating to improve water use efficiency and conservation in California by promoting smarter water infrastructure investments and the adoption of water reuse and recycling goals. That way, farms and communities have to rely less on natural waterways as water sources.

HABs have been a prevalent issue this summer in California lakes, rivers, and reservoirs. Unfortunately for Lilly and her owners, she didn’t recover from being poisoned by algal toxins, and she passed away. The risks that HABs pose to the health of communities, including people and pets, is too painful to ignore. There are many reasons California should mandate increased freshwater flows and less water pumping from its over-tapped rivers. The fact that waterbodies are made more susceptible to HABs by unsustainable water management is one of them.

About the Authors

Melanie Sturm

Program Assistant, Nature Program

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