What is fish passage?

Fish passage refers to the ability to effectively and efficiently allow fish to move through a water system, including successfully navigating human-made structures like dams and culverts, which can impede their journey. Whether fish need to migrate 10 miles or 1,000 miles, all fish species need to be able to move throughout water systems to access different habitats, food, and environments that support their life cycles. Fish passage technologies and approaches—such as fish ladders—play a critical role in maintaining sustainable fish populations and healthy aquatic ecosystems.

Dams, culverts, and other human-made structures on rivers and streams provide valuable services—for example hydropower dams may provide flood mitigation, water for drinking and irrigation, and clean renewable power. In 2021, hydroelectric power sources generated about 6 percent of total electricity generated in the United States, representing about 31 percent of U.S. renewable energy, and pumped storage hydropower provided approximately 93 percent of utility-scale energy stored in the U.S. These numbers could increase in the future as reliance on renewable sources of energy continues to grow.

Incorporating fish passage technologies and approaches with hydroelectric dams and other human-made river structures can support river connectivity and help fish navigate these barriers. That’s why multiple pieces of state and federal legislation support fish passage efforts, and the science of fish passage is an active area of research.  

Fish migration and fish passage

Some fish species, like salmon, migrate significant distances during their lives—traveling from the rivers and streams where they are born, to the ocean where food is abundant, and then back to freshwater spawning locations as adults. Other species—like walleye—migrate completely within freshwater systems to access seasonal habitats and food. Systems with multiple dams may have significant effects on fish species that travel long distances, especially if the dams do not have fish passage structures. Culverts, which carry water under structures such as roads, are smaller than dams but can also reduce or eliminate river connectivity and block fish movements and migrations.

History of fish passage

For thousands of years, indigenous peoples in the United States relied on fish—including salmon, lamprey, shad, and sturgeon—as key food sources with cultural and spiritual significance. The construction of large dams in the 20th century altered fish habitats and migration routes, making fish passage efforts critical to the sustainability of many fish species and the communities that rely on them. Multiple major dams were built without fish passage options, which made much of the historical habitat of migratory fish species inaccessible and spurred advocacy efforts by Tribes and conservation groups to bring concerns for fish to the forefront

Even though some state legislation supported fish passage as early as 1890, not all dams designed and built during the 20^thcentury were required to include fish passage. Fish passage efforts became part of federal legislation with the passage of the Federal Power Act in 1920, and multiple pieces of legislation since then have further supported fish passage in various ways, including the Endangered Species Act in 1973 and the Northwest Power Act in 1980. Federal agencies that manage hydropower dams are now required to mitigate impacts on fish and wildlife.

Significant investments have been made in research, development, and testing of improvements to fish passage for dams across the country by the Department of Energy (DOE), other federal agencies, and academic and industry partners. In 1999, the National Fish Passage Program facilitated by the U.S. Fish and Wildlife Service (FWS) was established to support fish passage projects. Since then, research and development in fish passage has grown with support from multiple agencies—including DOE, Department of Defense, Department of the Interior, National Oceanic and Atmospheric Administration (NOAA), FWS, and others—to advance fish passage options and fish friendly technologies across the country. Recently, the Infrastructure Investment and Jobs Act in 2021, also called the Bipartisan Infrastructure Law (BIL), included $200 million for restoring fish and wildlife passage by removing in-stream barriers and providing technical assistance under the National Fish Passage Program. In all, Congress appropriated more than $4 billion in the BIL to multiple agencies—including DOE, NOAA, Federal Emergency Management Agency (FEMA), the Bureau of Reclamation, United States Army Corps of Engineers (USACE), the Federal Highway Administration, and more—for improvements related to fish passage.

Many of the fish passage technologies and approaches used historically are still used today. In addition to fish ladders, which have long been used at dams, mechanized fish lifts were first implemented in some dams during the 1950s. Additional support for fish passage has led to the development of new approaches and efforts to accommodate passage a wider range of species—for example, the installation of eelways supports the passage of juvenile American eels and modifications to fish ladders accommodates species like lamprey that have different swimming patterns. Within just the last few years, advances in turbine design—like new shapes for turbine blades and wider spaces between blades—are also making downstream fish passage safer. Recently, there have been increased efforts to remove outdated, deteriorating, or defunct dams and structures as part of river restoration programs, which also improve fish passage.

In the last few decades, some fish species, such as salmon and steelhead, have been reintroduced to historical habitats that have been inaccessible for many years due to the presence of impassable dams and other structures. Fish passage is an active area of research, with scientists and partners developing new approaches and technologies to support the passage of more fish and other aquatic species through dams.

Why is fish passage important?

Dams, culverts, and other human-made structures in waterways provide important services and resources, including flood protection, water resources, and power generation. However, placing these structures in rivers and streams creates physical barriers for migratory fish and other aquatic species, contributing to the loss of habitat and migration routes. Water quality issues, such as pollution and fertilizer runoff, can also affect fish health, survival, and passage. Changes in water temperature, oxygen, nutrients, and other characteristics can also decrease the available fish habitat, creating conditions where fish cannot thrive, and impeding fish passage through certain areas. These factors have contributed to the significant declines in fish populations in the United States. Fish passage efforts can help overcome many of these challenges to support healthy fish populations and freshwater ecosystems.

In addition to being economically and ecologically valuable, some migrating fish species are also culturally important to Tribes. Key examples include salmon and lamprey in the Pacific Northwest and sturgeon in the eastern United States, which are considered “first foods” that play significant roles in ceremonies and food security. Without fish passage technologies and approaches, these and other fish species would not be able to successfully navigate human-made structures in rivers and streams to reach their spawning habitats and reproduce. That could have devastating consequences not only on the fish but also on the aquatic ecosystems and communities that rely on those fish.

The benefits of fish passage

Fish passage supports populations of fish and other aquatic species that are important economically, ecologically, and culturally to communities across the United States while maintaining critical infrastructure on waterways. For communities and groups that have experienced declining fish populations or complete loss of access to certain fish species, fish passage supports restoration and recovery that provides cultural benefits and helps to address environmental justice concerns. Efforts to improve fish passage can also help reduce the environmental impact of hydropower projects.

To support fish passage, researchers have developed new tools, such as improved sensor and receiver technologies to track and monitor fish passage through dams. Recent advances in autonomous receivers are enabling near-real-time data collection of fish location while also providing multi-sensor platforms that monitor environmental data and help researchers better understand the effects of climate change on river and stream ecosystems. These advances provide information far beyond fish passage that can impact planning and decision-making to sustain healthy waterways. Some fish passage technologies also have broad applications in other fields. For example, radio frequency tags, originally designed by Pacific Northwest National Laboratory (PNNL) researchers to track fish, are now widely used to track bats, insects, and other species.

Challenges in fish passage research and development

Fish passage research and development aims to provide appropriate passage options for a wide variety of species, improve tracking and monitoring of fish, and support information sharing with hydropower stakeholders. 

To design appropriate fish passage structures and identify dam operations that help increase fish survival, it is critical to understand fish biology and behavior around dams. Fish species have different swimming abilities and tolerances for water conditions, which can affect whether they use some fish passage structures. For example, not all fish species can successfully swim up a fish ladder, which is a common fish passage structure at dams. Some fish cannot tolerate the rapid changes in water conditions around dams—such as spikes in water pressure—which prevent them from safely passing through dams. Better understanding fish biology and behavior around dams will help inform the development of fish passage approaches that are more effective for more species.

Another challenge is tracking and monitoring fish to support adaptive, timely fish passage approaches. Currently, there is limited real-time information available to dam operators and regulators about fish movement and behavior. Without accurate, updated information about fish locations, it can be difficult for dam operators to adequately anticipate and accommodate large groups of fish traveling through or around dams. This also makes it challenging for researchers and managers to monitor fish passage and troubleshoot problems in a timely manner. Technological advances in fish tracking and monitoring are underway to close this gap and provide timely information to inform dam operations.

Information related to fish monitoring and behavior must also reach dam operators and regulators. Advanced decision support tools and resources, such as those developed by social science and human dimensions researchers, are necessary to relay critical data on fish monitoring and behavior to operators and regulators. These tools support informed decision-making that can help mitigate the environmental impacts of human-made river structures.

Fish passage also faces economic and social challenges. Designing and building fish passage structures for small-scale hydropower projects can be prohibitively expensive, while adding them to large, existing dams that were not designed to include fish passage structures is not always feasible. Socially, the connections between humans, fish, and water resources are complex, and the history of fish passage and dams reflects this. Historically, the placement of dams has negatively impacted certain communities—notably, some dams have curtailed or eliminated many Tribes’ access to important fish populations. Fish passage efforts can begin to address some of these environmental justice issues while simultaneously supporting healthy, resilient aquatic ecosystems important for long-term human health and vitality. 

Developments in fish passage

Researchers are working to provide data and advanced technology that will help improve fish monitoring and the environmental performance of dams and other structures, and provide valuable data and metrics to support informed planning and decisions.

Researchers are developing new technologies that will provide near-real-time data on fish movement to inform dam operators and help guide day-to-day operational decisions. A key goal for researchers in this area is to provide real-time data on fish location and movement to dam operators so they can make informed decisions at pivotal times. For instance, if a group of juvenile fish is approaching a dam, alerting the dam operators in real-time will help them make appropriate and timely decisions, which in turn supports greater fish passage.

Another key area of research is better understanding fish behavior around dams and other structures to improve more species’ survival and passage. In some rivers on the East Coast, specially designed pegboards have been installed to create eelways that facilitate the movement of eels up and over dams to access habitat. In the Pacific Northwest, lamprey often struggle to use fish ladders designed to support salmon because lamprey swim differently and often travel deeper in the water. Various approaches to better accommodate lamprey passage are being tested.

Other efforts are focused on altering turbine designs to help fish move safely through dams and developing improved bypasses and altering fish ladder designs to better support a broader range of migratory aquatic species. Since 2016, the U.S. Army Corps of Engineers has installed new turbines at multiple dams on the Columbia River that were specifically designed to improve fish passage. Fish passing through these new turbines are now estimated to have a survival rate of 98 percent, compared to around 90 percent with the previous turbine designs.

Fish passage at PNNL

PNNL is a leader in fish passage research, developing new approaches and technologies to support fish populations and lower the environmental impact of renewable hydropower.

With the support of DOE's Water Power Technologies Office (WPTO) and the USACE, PNNL researchers have developed multiple sensors, acoustic tags, and receivers to improve fish passage and provide critical information to dam operators in near-real-time. PNNL researchers developed micro acoustic tags that can now be used to track eel and lamprey, a tiny biosensor—called Lab-on-a-Fish—that can track fish health stats and locations, and a wireless autonomous receiver that can be placed in remote locations to provide hourly fish tracking information. The new acoustic receiver can also be used to deploy sensors that measure water quality conditions, providing information about the effects of climate change on fish and aquatic ecosystems.   

As part of WPTO’s HydroPASSAGE project, PNNL developed a suite of tools and technologies, including the Biological Performance Assessment and Hydropower Biological Evaluation Toolset, to help guide hydropower operations and decisions that impact fish passage. The project also supported the development of Sensor Fish, a cylindrical sensor that can collect data on the physical experiences of fish as they pass through dams to assess the impact of new turbine designs on fish passage. Underlying these technologies are biological response models that summarize how fish respond to physical stresses associated with turbines and other structures, like collisions and rapid water pressure changes. PNNL researchers have developed and collected models for more than 20 species of fish.

PNNL researchers also work to independently evaluate the efficacy of new approaches to fish passage, including alternative transport tubes, spillway weir redesigns, and other creative innovations and proprietary fish passage technologies.

In addition to direct research and development, PNNL hosted the international Fish Passage Conference in 2022, an annual meeting that convenes leading experts and stakeholders in fish passage. PNNL researchers also participate in the annual Salmon Summit, put on by the Benton Conservation District, which conducts outreach and education on fish passage science and technology for thousands of elementary school children every year.