The Role of Fish Passage Structures in River Health

It starts with a small dam, a seemingly harmless structure. The water spills over, creating a gentle cascade that feels picturesque to the human eye. But beneath the surface, this barrier is a fortress, stopping fish in their tracks and reshaping the ecosystem in ways we often fail to see. These structures halt the journeys of migratory fish like trout and salmon and disrupt the movements of non-migratory species, such as minnows, baitfish, and other small fish. To a shiner, dace, or darter species, a culvert set just a few inches too high might as well be Niagara Falls, an insurmountable barrier preventing access to essential habitats. For creeks and rivers, these barriers disrupt everything from water quality to biodiversity, creating far-reaching consequences for aquatic life and the surrounding environment.

To the untrained eye, a small head dam breaking a river's flow may seem like a picturesque spot for a photo or a picnic, but it’s a dead end to the fish trying to navigate upstream. Game fish like bass and catfish often rely on unfragmented waterways to reach ideal spawning grounds or escape challenging conditions, but barriers like these trap them in unsuitable habitats. Minnows and baitfish, crucial components of the aquatic food web, struggle to bypass such obstacles, depriving larger species of a critical food source. Countless creeks, streams, and rivers are fragmented by these types of barriers, big and small, leaving fish populations stranded and ecosystems out of balance. Without passage, these fish cannot access the habitat, conditions, or headwaters they need to spawn. Their lifecycle is interrupted by a seemingly minor obstacle.

The Hidden Consequences of Small Barriers

Small dams and improperly installed culverts often are overlooked. After all, they don’t dominate the landscape like hydroelectric dams. Yet their impact can be just as damaging. Culverts set too high above the streambed create small waterfalls that fish can’t leap. Over time, these structures fragment river systems, leaving fish populations isolated in smaller and smaller habitats.

While migratory fish like salmon and trout often take the spotlight, the impacts of these barriers also extend to non-migratory species. Minnows and baitfish struggle to navigate these obstacles. These tiny species often move within streams to find shelter, food, or calmer waters during changing seasons. When culverts create impassable steps, their populations can dwindle, leaving larger predatory fish without a steady food source. Over time, this disrupts the balance of the entire aquatic ecosystem.

The effects are just as severe for game fish such as bass and catfish. These species often rely on connected habitats to find optimal spawning sites or to escape adverse conditions like low oxygen levels or high temperatures. Fragmented waterways can trap populations in suboptimal areas, reducing their resilience and growth. Anglers may notice fewer fish or less healthy populations, a direct consequence of these hidden barriers.

Small head dams also exacerbate flooding by impeding natural water flow. In heavy rain events, water pools behind these barriers, increasing the risk of overflow and erosion. These impacts can be costly for landowners downstream, threatening roads, property, and farmland. These structures also alter sediment flow, leading to erosion downstream and sediment buildup upstream, further degrading rivers' natural function.

Fish Passage Structures: The Key to River Restoration

Fish passage structures are more than engineering solutions; they are lifelines for our creeks and rivers. Here’s how they work:

• Culvert Retrofits: Outdated culverts can be replaced or modified to ensure water flows naturally. By lowering the trench to match the streambed, we eliminate those fish-stopping falls and create a seamless passage. Retrofits can also include increasing the size to accommodate adequate flows or adding natural substrates to mimic stream conditions, ensuring that even the smallest fish can navigate upstream.
• Fish Ladders: Fish ladders are designed for more substantial barriers like dams. They provide a series of stepped pools that fish can swim through, one level at a time. Each step mimics a natural riffle, allowing fish to bypass obstacles. Advanced designs can also accommodate species with different swimming capabilities, ensuring a broader range of aquatic life benefits.
• Barrier Removal: In some cases, the best solution is complete removal. By tearing down unused dams or abandoned infrastructure, we allow rivers to flow freely, restoring their natural function. Barrier removal reconnects habitats and restores sediment flow, crucial for maintaining healthy streambed substrate.
• Nature-Like Fishways: These structures mimic the natural gradients of streams, providing gentle slopes and resting areas that all aquatic species, from minnows to larger game fish, can navigate easily. They are particularly effective in areas with diverse fish populations and varying needs.
• Partial Modifications: Sometimes, complete removal or replacement isn't feasible. Partial modifications, such as notching a dam or creating bypass channels, can still significantly improve aquatic connectivity while maintaining some of the benefits of the existing infrastructure.

Each of these solutions brings immediate and lasting benefits. For fish, it’s a chance to reclaim their ancestral migration routes. For landowners and communities, it’s an opportunity to reduce flood risks and improve water quality. For conservationists, it’s a tangible win in the fight to protect biodiversity. Beyond the ecological gains, these efforts also enhance recreational opportunities, supporting angling, boating, and ecotourism industries, which play a vital role in local economies.

A Ripple Effect of Benefits

When rivers are reconnected, the benefits cascade through the entire ecosystem. Consider the macroinvertebrates, the aquatic insects that form the base of the food chain. Healthy, connected streams allow these tiny creatures to thrive, providing essential food for fish, birds, and other wildlife.

Restoration efforts also improve recreational opportunities. Anglers benefit from healthier fish populations, while kayakers and boaters enjoy safer, more navigable waters. Even local economies see a boost; in regions where fishing and ecotourism are key industries, reconnecting rivers can bring in millions of dollars annually.

The Aquatic Connectivity Framework: A Partnership for Change

The ACF is leading the charge to remove barriers and restore aquatic ecosystems across 16 states, from the Gulf Coast to the Appalachian Mountains. By partnering with private landowners and leveraging USDA resources, the framework provides technical and financial assistance for culvert retrofits and dam removals. Together, communities envision healthier waterways and take steps to make that vision a reality.

A Call to Action

Imagine a river flowing freely, its waters clear and unobstructed, supporting fish and wildlife without interruption. Removing outdated barriers that no longer serve a purpose is the first step toward reconnecting rivers to their natural rhythms and restoring the ecosystems they sustain.

Whether you’re a landowner, an angler, or simply someone who loves the outdoors, you have a role. Visit your local NRCS office, explore the Aquatic Connectivity Framework online, or use the AquaCorridors Compass to learn how you can get involved. Together, we can ensure our rivers remain wild, resilient, and full of life—for generations to come.