Rethinking Wetland Restoration: UC Davis Research Challenges Traditional Conservation Practices

A decade of research suggests that simply restoring wetlands to tidal systems may not always produce the best outcomes for native fish and wildlife.

Wetlands are among the most productive ecosystems on Earth. They filter water, reduce flooding, store carbon, provide habitat for hundreds of species, and serve as critical nurseries for fish, birds, amphibians, and countless other forms of wildlife.

For decades, conservation efforts have focused on restoring wetlands that were altered or drained by human activity. The assumption has often been straightforward: return wetlands to a more natural tidal state, and native wildlife will return.

But new research from the UC Davis Center for Watershed Sciences suggests the answer may not be quite that simple.

After nearly 10 years of studying wetlands in California's Sacramento-San Joaquin Delta and Suisun Marsh, researchers have found that some traditional restoration practices may unintentionally create habitats that favor invasive fish rather than the native species conservationists are trying to protect.

The findings are encouraging scientists, resource managers, and restoration professionals to rethink how wetlands are designed—not whether they should be restored, but how restoration can produce the greatest ecological benefit.

Wetlands Are More Than Just Marshes

Wetlands are often thought of as quiet marshes filled with reeds and birds, but they perform a remarkable number of ecological functions.

Healthy wetlands:

• Improve water quality by filtering pollutants.

• Reduce flooding by storing excess water.

• Recharge groundwater supplies.

• Capture and store carbon.

• Support fisheries and aquatic food webs.

• Provide habitat for migratory birds, amphibians, reptiles, mammals, and fish.

In California alone, wetlands are essential for hundreds of wildlife species, many of which are threatened or endangered.

Because so much historic wetland habitat has been lost over the past century, restoration has become one of the state's highest conservation priorities.

The Study

Researchers from the UC Davis Center for Watershed Sciences evaluated fish populations in several types of wetland habitats, including managed wetlands, restored tidal wetlands, and slough channels within Suisun Marsh.

In a complementary study, the team also examined Dutch Slough, one of California's largest tidal wetland restoration projects.

Rather than looking only at vegetation or water movement, scientists focused on how different restoration designs influenced fish communities, water quality, and plankton—the tiny organisms that form the base of aquatic food webs.

The research represents the culmination of nearly a decade of field surveys, biological sampling, and ecological monitoring.

Surprising Results

Many restoration projects are designed to reconnect wetlands with natural tidal flows.

While this approach often recreates historic conditions, researchers found that these restored habitats frequently became dominated by invasive fish species.

Managed wetlands, on the other hand, consistently supported larger numbers of native fish.

One species that particularly benefited was the three-spined stickleback, a small native fish that plays an important role in wetland ecosystems by serving as prey for larger fish, birds, and other wildlife.

These findings suggest that restoration success cannot be measured simply by recreating tidal conditions.

Instead, scientists argue that habitat quality for native species should remain the primary goal.

Design Matters

One of the study's most important conclusions is that restoration design can significantly influence ecological outcomes.

Researchers found that wetlands incorporating diverse habitat features often performed better than those relying on a single restoration model.

Features such as:

• Open-water habitat

• Varied water depths

• Improved connections to surrounding waterways

• Diverse shoreline structure

• Healthy plankton communities

all appeared to influence how fish populations responded.

Rather than treating every restoration project the same, the researchers recommend designing wetlands to match the ecological needs of native wildlife.

Why Invasive Species Thrive

Invasive fish often possess characteristics that allow them to quickly colonize newly restored habitats.

Many reproduce rapidly, tolerate changing environmental conditions, and compete aggressively for food and shelter.

When restoration unintentionally creates ideal habitat for these species, native fish may struggle to establish healthy populations.

This doesn't mean restoration has failed—it simply means ecological responses are often more complex than expected.

By understanding these patterns, scientists can improve future restoration projects before large investments are made.

Why This Matters for Veterinary Medicine

At first glance, wetlands may seem far removed from veterinary medicine.

In reality, they are deeply connected.

Healthy wetlands support fish, amphibians, reptiles, waterfowl, shorebirds, mammals, and countless invertebrates. Many wildlife veterinarians, aquatic animal specialists, and conservation biologists depend on healthy wetland ecosystems to sustain the species they study and protect.

Wetlands also influence disease ecology.

Changes in habitat can affect mosquito populations, water quality, migratory bird behavior, and interactions among wildlife species, all of which may alter the transmission of infectious diseases.

For veterinarians working in wildlife health, ecosystem management, or conservation medicine, habitat quality is often just as important as clinical care.

The study reinforces the growing recognition that protecting animal health begins with protecting healthy ecosystems.

A One Health Perspective

The findings also illustrate the principles of One Health.

Environmental changes influence wildlife populations, which can affect domestic animals and, ultimately, human communities.

Wetlands provide drinking water protection, flood control, fisheries, recreation, and biodiversity. When these systems function well, they benefit entire communities—not just wildlife.

Scientists increasingly recognize that conservation decisions should be based on long-term ecological monitoring rather than assumptions about what restored habitats should look like.

A New Direction for Restoration

Lead researcher John Durand believes the studies point toward a more adaptive approach to restoration.

Instead of applying one restoration strategy everywhere, future projects should incorporate multiple habitat types and remain flexible as new scientific information becomes available.

The research also highlights the value of long-term monitoring.

Many ecological changes unfold over years rather than months, making decade-long studies essential for understanding whether restoration projects are meeting their goals.

As climate change, sea-level rise, and urban development continue to reshape aquatic ecosystems, evidence-based restoration will become increasingly important.

Looking Ahead

Wetland restoration remains one of conservation's most powerful tools.

The UC Davis research does not argue against restoring wetlands—it argues for restoring them more thoughtfully.

By carefully designing habitats that support native species while limiting opportunities for invasive fish, conservationists can improve biodiversity, strengthen aquatic ecosystems, and maximize the return on restoration investments.

For veterinarians, wildlife professionals, and environmental scientists, the message is clear: protecting wildlife requires more than restoring landscapes. It requires understanding how ecosystems function and using science to guide every step of the restoration process.

Healthy wetlands don't just support healthy fish—they support healthy birds, mammals, amphibians, people, and the ecosystems that connect them all.