Recent flooding along the Long Beach Peninsula has brought renewed attention to the area’s changing shoreline. With dredging now underway near the entrance to Alamitos Bay and sand being placed along Peninsula Beach, it’s easy to assume the project is a direct response to these recent events.
In reality, the project has been years in the making. It addresses two longstanding issues: sediment accumulation in the Alamitos Bay entrance channel and erosion along Peninsula Beach.
The project also offers an opportunity to explore how decades of coastal engineering have influenced the movement of sand along our shoreline, and what environmental considerations are involved when we intervene in these natural processes.
Maintaining the Alamitos Bay Entrance
Sediment is constantly moving along our coastline, carried by waves and currents. While some areas experience erosion, others accumulate sand and sediment over time.
At the entrance to Alamitos Bay, sediment has gradually accumulated on the seafloor. A July 2023 underwater survey found that most of the entrance channel was shallower than the City’s target maintenance depth of 20 feet. The survey identified approximately 270,500 cubic yards of sediment above that target depth.
The City of Long Beach is dredging the entrance channel to a depth of 20 feet below mean lower low water, a standard tidal reference level. According to the City, the purpose is to maintain safe navigation for vessels traveling between Alamitos Bay and the ocean.
The entrance channel had not been dredged for more than 20 years.
Importantly, the dredging is limited to the entrance channel, not the interior of Alamitos Bay. The project is intended to maintain the navigation channel rather than deepen the bay as a whole.
Explore the City’s engineering plans and underwater survey maps.
A Long History of Dredging and Shoreline Management
Dredging at the Alamitos Bay entrance is not a recent practice. Historical records document dredging near the entrance as early as 1938.
During 1945–1946, approximately 800,000 cubic yards of sediment were removed as part of the construction of a new entrance channel. Much of that material was placed along nearby beaches. Additional dredging occurred in 1950, again with sediment used to replenish the Peninsula shoreline.
These early projects illustrate how navigation maintenance and beach nourishment have been connected at Alamitos Bay for generations.
The Long Beach Public Library’s historical collection includes a photograph of dredging near the entrance in 1938. A historical coastal engineering study provides additional information about the area’s dredging and shoreline management history.
Why Peninsula Beach Continues to Erode
While sediment has accumulated at the entrance channel, Peninsula Beach has experienced chronic erosion for decades.
According to the California Coastal Commission, this erosion dates back to the development of Alamitos Bay in the early 1920s. The construction of jetties near the bay entrance and San Gabriel River interrupted the natural east-to-west movement of sand along the coastline. The Long Beach breakwaters further altered wave conditions and sediment transport.
These structures helped create the coastline and waterways we recognize today, but they also changed the natural processes that replenish our beaches.
The current project uses sediment removed from the entrance channel to replenish Peninsula Beach, a process known as beach nourishment. Adding sand can widen the beach and provide a buffer against wave impacts, although it does not eliminate the forces responsible for erosion.
Although planning and environmental review for this project began well before the recent flooding, the damage along Peninsula Beach highlights the shoreline’s ongoing vulnerability. The project is one approach to managing that vulnerability, rather than a permanent solution to the coastal processes affecting this area.
Read the California Coastal Commission’s discussion of Peninsula Beach erosion and project history.
What the Project Involves
The project authorizes the removal of up to approximately 415,000 cubic yards of sediment from the Alamitos Bay entrance channel.
Suitable dredged material is transported through a pipeline to Peninsula Beach, where it is distributed along the shoreline to replenish areas affected by erosion.
The project is designed to address navigation maintenance and shoreline nourishment together, making use of sediment that would otherwise need to be managed or disposed of elsewhere.
View the project boundaries and beach nourishment areas.
Evaluating Potential Environmental Impacts
Moving hundreds of thousands of cubic yards of sediment in a coastal environment raises important questions about water quality, marine habitats, and the organisms that live on and beneath the seafloor.
Before construction, environmental consultants collected sediment samples from 20 locations across five dredging areas. These samples were tested for pollutants and potential effects on marine life to determine whether the material was suitable for beach nourishment.
Sediment testing detected chlordane, a pesticide that was widely used decades ago, in sediment from one area of the channel. The concentration was slightly above an environmental screening level used to identify possible concerns.
This finding is not entirely new for Alamitos Bay. Earlier studies conducted in the 2000s and 2010s also detected chlordane and other pollutants in sediment from parts of the bay and nearby waterways. These findings reflect a history of pollution that predates the current dredging project.
Scientists also tested whether the sediment was harmful to small organisms that live on or near the seafloor. The tests did not find significant short-term toxic effects in the organisms studied. Based on the overall testing and environmental review, the Southern California Dredged Material Management Team determined that the sediment was suitable for beach nourishment. As an added precaution, sediment from the area with elevated chlordane must be placed beneath sand from other dredging areas.
Read the current project’s sediment testing and environmental findings.
Read the Long Beach Nearshore Watershed Management Program’s historical sediment findings.
Eelgrass Habitat
Eelgrass provides important habitat for fish and other marine life. Surveys conducted in March and April 2024 identified approximately 184 square feet of eelgrass near the project site.
The dredging area was designed to avoid directly disturbing these plants, with a buffer of approximately 70–100 feet from most nearby eelgrass beds.
Because eelgrass can spread or change over time, the project requires an updated survey before construction. If the work is expected to affect eelgrass, additional permitting is required. Follow-up surveys and restoration may also be necessary if impacts occur.
Read the eelgrass findings and permit requirements.
Water Quality and Turbidity
Dredging can temporarily stir up sediment, making the surrounding water cloudier. This is known as turbidity. When turbidity increases, less sunlight can reach underwater plants, and fish and other marine animals may have more difficulty finding food.
To limit these impacts, the project requires that turbidity not increase by more than 20% above natural levels during non-storm conditions. Barriers called silt curtains must also be used to help contain suspended sediment wherever practical.
Read the water quality requirements, Special Conditions 9–10.
Dissolved Oxygen
Fish and other aquatic organisms depend on oxygen dissolved in the water to survive. Construction activities can affect oxygen levels, particularly when sediment is disturbed.
The project requires that dredging activities not cause dissolved oxygen levels to fall below 5.0 milligrams per liter, a threshold intended to protect aquatic life.
Read the dissolved oxygen requirement, Special Condition 9.
Coastal Birds and Other Wildlife
The project also includes protections for sensitive wildlife, including the western snowy plover, California least tern, California brown pelican, and California grunion.
During relevant breeding periods, surveys are required within the construction area and a surrounding 500-foot buffer. A qualified biological monitor must be present during applicable work and has the authority to stop activities when necessary to protect wildlife.
Beach nourishment is generally restricted between February 15 and September 15, unless additional authorization is obtained following an assessment of potential impacts to protected species and grunion spawning.
Read the wildlife protection requirements, Special Conditions 4–5.
Understanding the Remaining Impacts
The California Coastal Commission approved the project in June 2025, and the U.S. Army Corps of Engineers issued its authorization later that summer.
The environmental studies and permit requirements establish important safeguards, but they do not mean dredging will have no ecological effects. Removing sediment disturbs the seafloor and the organisms living within it, while construction activities can temporarily change surrounding water conditions.
The environmental review helps establish what must be protected and how the work should be carried out. Understanding what actually happens during construction, however, requires looking at the results of environmental surveys and monitoring.
For example, the publicly available Coastal Commission report identifies the need for an updated eelgrass survey and establishes water-quality protections, but it does not include the results of that updated survey or measurements collected during dredging.
These results will be important for understanding how conditions compare with those documented before construction and whether the project’s environmental protections are working as intended.
Understanding Our Changing Coastline
The Alamitos Bay dredging project reflects a much larger story about the relationship between coastal development and natural processes.
Over the past century, jetties, breakwaters, navigation channels, and shoreline development have reshaped the movement of water and sediment along this stretch of coast. Dredging and beach nourishment are among the ways we continue to manage those changes.
As coastal communities face ongoing erosion, flooding, and rising sea levels, understanding the consequences of past engineering decisions, and the environmental implications of current projects, becomes increasingly important.
While environmental studies and permit requirements establish important safeguards, understanding the project’s actual ecological effects also requires examining what happens before, during, and after construction.
Algalita is currently seeking additional information about the project’s biological surveys and environmental monitoring, including pre-construction eelgrass assessments, water-quality measurements, and any required post-construction surveys. We’re interested in understanding what these assessments reveal about environmental conditions and how those conditions may change as a result of the project.
Through Clean Bay Collective, community scientists are also collecting water-quality data throughout Alamitos Bay. Although this monitoring is independent of the dredging project, it contributes to a broader understanding of conditions in this changing coastal ecosystem.
We’ll continue to follow the project and share updates as additional survey results and monitoring information become available.