California’s Freshwater Challenges: Looking Ahead to 2025 and Beyond

“The health of our rivers is the principal measurement of how we live on the land.” — Luna Leopold. 

Most of life on Earth relies on freshwater. In California, our freshwater systems are facing serious challenges. Dams, pollution, and land development have severely degraded rivers and freshwater ecosystems. These factors have led to a decline in our freshwater species and biodiversity, which are crucial for maintaining healthy and resilient ecosystems. The health of our freshwater rivers directly impacts our communities and California’s economy, making it essential to protect and restore these precious freshwater resources. Fortunately, over the last 20 years, California has demonstrated vision and commitment in protecting our state’s land and waters. Numerous plans have identified potential actions to safeguard our rich biodiversity. 

California Rivers  

Loss of Freshwater: Dams, Development, and Pollution 

Over 1,400 dams exist on our rivers, with only one major river (the Smith River) in California completely undammed. These dams and infrastructure impact the natural flow of rivers, affecting ecosystems and the species that depend on them. Dams physically block the flow of rivers, preventing the natural movement of the water downstream, altering the natural flow and processes that keep freshwater ecosystems healthy. Dams can also alter the timing and volume of water released downstream. For example, dams with hydropower often release water to generate electricity during peak demand periods, which can create an unnatural flow pattern. These irregular release patterns can disrupt the natural seasonal flow patterns that fish, vegetation, and aquatic life depend on for growth and reproduction. Loss of natural flow also means that sediment gets trapped behind the dam and accumulates in the reservoir rather than being transported downstream, where it is needed to create and maintain habitats for aquatic species and salmon that rely on these areas for spawning and feeding. Dams can significantly alter the natural water temperature regime in a river. Water that is released from the bottom of a reservoir is often much colder than the natural river water during warmer months and warmer during colder months. This unnatural temperature regime can also have harmful impact on aquatic species and fish.  

Rivers aren’t the only freshwater resource harmed by our management decisions. Wetlands, which are characterized as areas of wet soil that are frequently covered by water or saturated, also face threats from human land management and climate change. Our land use choices and development policies have caused the loss of the vast majority of our state’s wetlands which play a crucial role in maintaining water quality. Over 90% of California’s wetlands have disappeared, and their absence has had profound impacts on both water quality and ecological health. Wetlands are essential for filtering pollutants and providing habitat. One significant example is California’s Delta which is in decline. A major factor in that decline is the loss of productive wetlands due to decreased freshwater as a result of dams, diversions, and other water infrastructure. Without freshwater, the Delta loses crucial habitat that supports migrating birds, fish, and other wildlife.

Overallocation of water reduces the natural flow in rivers and wetlands. These reduced water levels can increase water temperatures and decrease oxygen levels, making it difficult for fish and aquatic species to survive. Higher water temperatures can also promote harmful algal blooms (HABs), which deplete oxygen levels and create dead areas where aquatic life cannot survive. Contaminants from agricultural runoff such as pesticides, fertilizers, and nutrients harm water quality. Water runoff from paved surfaces can introduce heavy metals, chemicals, and other toxins into waterways, posing threats to fish and humans.  

Degraded Rivers 

As a consequence of our actions over the last century, a significant amount of our rivers across the state are classified as impaired, meaning the waterways do not meet water quality standards and are affected by pollutants, impacting their ability to support beneficial uses such as drinking water, agriculture use, swimming, and habitat for fish. A portion of the South Fork Yuba River (between Spaulding Dam and Englebright Dam) is on the state’s impaired 303d list primarily due to elevated water temperatures and mercury contamination.  These high water temperatures, especially during spring and summer, negatively impact native rainbow trout. 

Impacts to Plants and Animals 

Dams, loss of wetlands, and poor water quality have a profound impact on native freshwater species in California, contributing significantly to their decline. Of the 1,728 native freshwater species in our state, 482 (28%) are considered imperiled.   

“California’s freshwater ecosystems are in urgent peril, with nearly half of the state’s freshwater species vulnerable to extinction.” – Public Policy Institute of California 

Fish are among the most impacted, with 80% of native species considered imperiled. According to the Sierra Forest Legacy, six of the 40 native fish of the Sierra Nevada are listed as threatened or endangered and only half of the 40 species have secure populations (Moyle et al. 1996). Notably, several of California’s native trout, including the Little Kern golden trout and Lahontan and Paiute cutthroat trout, are at significant risk. The situation is equally dire for amphibians, with half of the 29 native amphibian populations in the region at risk of extinction. 

Several freshwater species in the Sierra Nevada are especially vulnerable due to habitat loss, pollution, and invasive species including the Mountain Yellow-Legged Frog, Lahontan Cutthroat Trout, and Yosemite Toad.  

Extinction rates for freshwater species are alarmingly high, with freshwater fauna about five times greater than those projected for terrestrial fauna. These sobering statistics underscore the urgent need to address our freshwater challenges and implement effective measures to protect these ecosystems.   

Biodiversity Matters 

Research over the last three decades has shown that biodiversity plays a key role in how our rivers and freshwater ecosystems function. Diverse ecosystems are more stable and productive; capturing carbon, producing oxygen, and cycling nutrients. Healthy meadows in our headwaters act as carbon sinks, capturing carbon dioxide and storing it in the plants and soil. As we face climate change and a depleting snowpack, these healthy meadows can capture water, helping to regulate water availability. Plants and vegetation growing on the banks of our rivers are critical during flooding, helping to control erosion and water quality while also serving as refuge for juvenile salmon. When fish return home to spawn they bring nutrients from the ocean back to freshwater ecosystems. These nutrients support the soil and aid in plant growth, which in turn supports a rich and diverse ecosystem of plants and animals.  

Research also shows that the loss of biodiversity can disrupt these vital processes, leading to a less efficient and resilient ecosystem, with that loss exacerbating those negative impacts and leading to other potential cascading effects.  

Community and Economic Health 

California’s $3 trillion economy heavily relies on access to clean water, and healthy freshwater ecosystems are key in maintaining water quality. On a community and regional level, freshwater is the lifeblood of our communities, providing water to drink, rivers to swim in, fish to eat, and areas for families to visit. For Indigenous communities, freshwater fish are essential for food security and hold cultural significance. The plummeting populations of salmon have had significant impacts on the health and socioeconomic well-being of Indigenous peoples in northern California. Protecting and restoring our freshwater ecosystems is not only crucial for environmental health but also for the cultural and economic health of our communities.  

In summary, freshwater ecosystems provide food and water (direct benefits), natural water filtration and flood control (socio-economic benefits) and recreational opportunities and aesthetic value (community and cultural benefits). In this way, our freshwater rivers provide “ecosystem services” that are essential for sustaining human life and environmental health. The natural processes of river ecosystems are crucial for their sustainability and the well-being of the communities that rely on them for resources and ecosystem services.  

Challenges on the Horizon   

Climate change poses significant threats to biodiversity. The combined impacts of climate change – rising temperatures, changing precipitation patterns, fires and droughts — can contribute to a decline in biodiversity, making our freshwater resources increasingly vulnerable to climate impacts.

At the same time, biodiversity is a key tool in cultivating climate resilience, enabling our freshwater ecosystems to withstand and thrive in the face of a more unpredictable and extreme climate.  

Conclusion 

California’s freshwater ecosystems face numerous challenges, including the impacts of dams, pollution, and unsustainable water management practices. These factors have significantly degraded our freshwater rivers, resulting in the decline of native species and the overall health of these vital ecosystems. Protecting and restoring these ecosystems is crucial, not only for the environment but also for the economic and cultural well-being of California’s communities  

In the face of these challenges, it is incumbent on our state’s leaders to take action to protect our freshwater rivers and mitigate the effects of climate change. Together, we can prioritize and take action to secure a healthier future for our freshwater rivers and the communities that depend on them.  We’ll outline how you can make a difference for freshwater protection through California’s 30×30 Plan in a future post on SYRCL’s website.

For more information:  

• Below the Surface: California Freshwater Diversity, The Nature Conservancy, May 2013 
• How’s My Waterway? Explore, Discover, and Learn about your water. U.S. EPA 
• Link: How’s My Waterway – State