Tred Avon River and Harris Creek Oyster Reef Restoration Updates

Oyster restoration efforts are part of the Maryland and Virginia statewide oyster restoration program, as laid out by the Corps’ Native Oyster Restoration Master Plan that identifies the most suitable tributaries throughout the Chesapeake Bay for large-scale oyster restoration based on physical and biological conditions. Work includes constructing 1-foot reefs using mixed-shell materials and rock.

The shell comes from coastal processing plants and is permitted to be imported and placed in the river. The rock is quarried in Havre de Grace, Maryland. The Corps and its partners engage with the Maryland Watermen Association as well as have a seat on the Oyster Advisory Commission, which allows them to discuss plans for restoration and receive feedback on how to mitigate for any potential concerns stakeholders may have. 



Tred Avon RiverThe U.S. Army Corps of Engineers, along with partners the Maryland Department of Natural Resources, the National Oceanic and Atmospheric Administration and the Oyster Recovery Partnership resumed construction of oyster reefs in Apr. 2021 in the Tred Avon River Oyster Sanctuary in Talbot County, ushering in the final stage of initial oyster restoration for the sanctuary. 

Approximately 34 acres of reef will be restored throughout the sanctuary using rock in water depths at least 6.75 feet mean lower low water (MLLW). Of those 34 acres, 21 acres will be built 12 inches in height using stone 3 to 6 inches in size with the remaining 13 acres to the built 6 inches in height using smaller stone 2 to 4 inches in size to help mitigate any potential impacts to navigation.

To date, 92.5 acres of reef have been restored in the Tred Avon with 440 million seed oysters planted.    

Read more about spring 2021 Tred Avon River construction efforts, including restoration construction maps and alternate substrate oyster reef coordinates here. Please be vigilant when navigating through these areas as water depth are 1 foot to up to 2 feet shallower than what is currently shown on navigational charts. NOAA is revising the charts to reflect these restoration areas and depth.       


Harris CreekAll planned restoration was completed in Harris Creek in summer 2015. Initial restoration was completed on approximately 350 acres with 2.46 billion oyster seeds planted. 

View the Harris Creek Oyster Restoration map that identifies where the Corps and Maryland DNR have placed rock and shell to restore oyster habitat in Harris Creek oyster sanctuary. In the areas identified, water depths are 1 foot to up to 2 feet shallower than what is currently shown on navigational charts. NOAA is revising the charts to reflect these restoration areas and depths. 




The Corps takes any impediments to navigation seriously and has developed a process to more efficiently conduct post-construction surveys before the spat-on-shell is placed, and is also tightening quality-control procedures with contractors for future work to ensure reefs are built to the planned heights. Efforts include ensuring contractors use a consistent bucket size for material deployment and marking the depth on the bucket cable as an additional visual cue.

Mariners should heed their USCG local notices. 


Oyster Reef Monitoring Results: The 2017 Oyster Reef Monitoring Report, published in November 2018, provides data and analysis that show that 100 percent of reefs constructed in the Harris Creek Oyster Sanctuary in 2014 and monitored in 2017 meet the requirements for oyster density (at least 15 oysters per square meter) and biomass. There were 14 eligible reefs studied. Restored reefs are monitored at three years and again at six years. 


2019 Maryland Oyster Restoration UpdateThe annual update on large-scale oyster restoration efforts in Maryland was published in March 2020. This summary of work, developed by the Maryland Oyster Restoration Interagency Workgroup, quantifies what was accomplished in 2019, as well as includes blueprint drafts for the two newly selected restoration tributaries, the Manokin River and the Upper St. Mary's River.  

U.S. Army Corps of Engineers, Maryland Oyster Restoration Overview

Oyster populations in the Chesapeake Bay have declined dramatically in the last century, largely due to parasitic diseases, overharvesting, declining water quality, and a loss of habitat. Less than one percent of historic oyster populations remains. Oyster restoration is important because oysters provide a number of environmental benefits, including reef habitat that is significant to the Bay ecosystem for animals like blue crabs and fish. Additionally, oysters are filter feeders that improve water quality.


The Native Oyster Restoration Master Plan is the Corps' plan for large-scale, sanctuary-based oyster restoration throughout the Chesapeake Bay and its tributaries in Maryland and Virginia. The master plan examines and evaluates the problems and opportunities related to oyster restoration, and formulates plans for implementing large-scale, Bay-wide restoration.


Project elements include: (1) creation of disease-free spat (oyster seeds or baby oysters) from state-owned hatcheries; (2) creation of new oyster habitat; (3) rehabilitation of existing non-productive oyster habitat; (4) construction of seed bars or reefs for production and collection of spat; (5) planting spat on the new and rehabilitated reefs; and (6) monitoring of project performance.

The Corps restores reef structure to re-establish oyster habitat where it previously existed. Maryland Department of Natural Resources produces the spat-on-shell (baby oysters) at the state-owned Horn Point Hatchery and provides for the planting of the spat-on-shell at restoration sites by the Oyster Recovery Partnership. The National Oceanic and Atmospheric Administration maps available restorable water bottom using sonar in conjunction with various ground‐truthing methods and also funds the production and planting of spat-on-shell.

Restoration only takes place in pre-existing sanctuaries, as established by Maryland DNR. Sanctuaries are areas that are closed to harvest; however, oysters within sanctuaries are expected to increase the abundance of adult oysters whose larvae settle not only within the sanctuary, but also on public shellfish fishery areas in the vicinity of the sanctuaries.

Typically, there are two barges used for constructing the reefs: one barge holds the substrate (reef material, such as rock or mixed shell), the other holds a crane with a bucket to move the substrate. The bucket picks up the substrate from the barge, then, with a sweeping motion, releases it into the water. GPS locaters are used to make sure the reefs are constructed in the selected sites. Spat-on-shell are brought from hatcheries and placed or “planted” on the constructed reefs in hopes of restoring the oyster population in these areas. Once planted, the oyster reefs are monitored to assess the restoration progress.

The Corps is involved in oyster restoration in two ways. Through an authority under Section 704(b) of the Water Resources Development Act (WRDA) of 1986, as amended, the Corps provides construction assistance for certain oyster restoration projects through its Civil Works program. For work undertaken by others, the Corps evaluates the impact of material placed into Waters of the United States under Section 404 of the Clean Water Act and Section 10 of the Rivers and Harbors Act, through a permitting process managed by the Corps Regulatory Program.

The Maryland project cooperation agreement was executed in February 1997, with an amendment in July 2002. Placement locations in Maryland include Kedges Strait, Eastern Bay; and the Chester, Choptank, Magothy, Patuxent, Severn and Tred Avon rivers - a total of approximately 600 acres of new oyster bars. Some of the oyster bars were left for natural recruitment; others received hatchery-raised spat. The Virginia project cooperation agreement was executed in September 2001, with amendments in July 2004 and June 2007. The Corps' Norfolk and Baltimore districts support activities in Virginia and Maryland, respectively. In Virginia, activities include oyster bar creation in Tangier Sound, Pocomoke Sound, the Great Wicomico River, and the Lynnhaven River - a total of approximately 400 acres of new oyster bars.

Prior to the 2009 restoration activities, the Corps oyster restoration program did not focus on large-scale tributary restoration in Maryland, as it does now.  From 1997 to 2006, the Baltimore District received relatively small funding allocations for a number of small sites, scattered throughout the Maryland portion of the Chesapeake Bay.  An assessment of the sanctuary sites constructed during this period was prepared and can be found in the September 2011 report, 2008 Sanctuary Assessment.

Oyster Restoration Larval Transport Model

This video shows a model of the movement of oyster larvae in Harris Creek. As you can see, the benefits of restoration extends beyond the sanctuary boundaries and into areas that can be harvested.

Additional Maryland Oyster Restoration Information

Authorization: Section 704(b) of the Water Resources Development Act of 1986, as amended.

Type of Project: Aquatic Ecosystem Restoration

Contribution to the Chesapeake Bay: Directly contributes to Executive Order 13508 goals to restore clean water, recover habitat, and sustain fish and wildlife. Also aligns with the Chesapeake Bay Watershed Agreement's goal to restore oyster reefs in 10 tributaries by 2025 - five in Maryland and five in Virginia. 

Project Phase: Construction

Non-Federal Sponsor: Maryland Department of National Resources in Maryland and Virginia Marine Resources Commission in Virginia

Point of Contact

Baltimore District Public Affairs