Potential Impacts of Offshore Wind on the Marine Ecosystem and Associated Species: Background and Issues for Congress

Offshore wind energy is one alternative to energy derived from the combustion of fossil fuels. The United States' ability to harness wind energy from the outer continental shelf (OCS) is at an initial stage compared with European countries and some Asian countries. As interest in the potential benefits of offshore wind grows in the United States, some stakeholders have expressed concerns about offshore wind projects' potential impacts on the marine ecosystem.

Offshore wind projects may affect the marine ecosystem and associated species in ways both adverse and beneficial. Stakeholders commonly cite effects such as changes to the ocean environment; habitat alterations; risks that living marine resources may collide with construction vessels and offshore wind structures; altered behaviors and disturbance of migration paths of certain fish, marine mammals, and birds; and water pollution. Some observers emphasize that, although individual offshore wind energy projects may have local, immediate impacts to certain species, the global ocean and the wildlife it supports are threatened by the long-term consequences of climate change. Many scientists concur that renewable power is important for addressing climate change and reducing its longer term environmental impacts. Some stakeholders have encouraged decisionmakers to include climate change risks facing the ocean and certain marine animals in analyses of offshore wind projects.

The National Environmental Policy Act (NEPA; 42 U.S.C. §§4321 et seq.) requires federal agencies to evaluate the impacts of major federal actions significantly affecting the human environment, such as issuing permits for offshore wind projects on the U.S. OCS. The Department of the Interior's (DOI's) Bureau of Ocean Energy Management (BOEM) is the lead agency for the preparation of environmental impact statements (EISs) in the context of approving developers' construction and operations plans for offshore wind energy projects. BOEM's responsibilities also include coordinating interagency review and permitting timelines in accordance with provisions of the Fixing America's Surface Transportation Act (42 U.S.C. §§4370m–4370m12). Certain federal agencies have further been tasked with administering specific statutes that aim to protect particular aspects of the environment or certain natural resources. The National Oceanic and Atmospheric Administration's National Marine Fisheries Service (NMFS) cooperates in the EIS processes pursuant to its responsibilities under the Endangered Species Act (ESA; 16 U.S.C. §§1531-1544) and the Marine Mammal Protection Act (16 U.S.C. §§1361-1423h). DOI's U.S. Fish and Wildlife Service considers the ESA and the Migratory Bird Treaty Act of 1918 (16 U.S.C. §703) when participating in EIS processes. Other agencies may also have responsibilities related to permitting and environmental review of offshore wind projects.

The U.S. Department of Energy lists 59 offshore wind projects in federal and state waters at various stages of development, ranging from conception to construction to fully commissioned. In federal waters, BOEM has issued more than 30 leases for offshore wind development (some covering multiple projects) and anticipates completing review of at least 16 construction and operations plans by 2025. Several projects are currently operating in state and federal waters in the Atlantic region. Two commercial-scale projects in federal waters off Massachusetts and Rhode Island—Vineyard Wind 1 and South Fork Wind—have begun delivering power. A two-turbine pilot project operated by Dominion Energy is generating electricity in waters off Virginia. The five-turbine Block Island project is operating in state waters off Rhode Island.

In the 118 th Congress, some Members have called for additional research into the potential harm offshore wind projects may cause to marine wildlife or expressed concern about the impacts that offshore wind activities might have on other ocean uses (e.g., H.R. 1 ). The full impacts of offshore wind activities on the U.S. OCS remain unclear, in part because the development of U.S. offshore wind projects is relatively recent. Issues for Congress may include potential impacts of offshore wind development on the marine ecosystem and potential long-term benefits of climate change mitigation derived from offshore renewable energy versus the immediate, local impacts of offshore wind to the marine ecosystem and associated species. Other concerns may include the potential loss of fishing grounds, interruptions to NMFS surveys, incidental take (or unintentional killing) of birds, and increased vessel activity that may be associated with offshore wind projects.

Development of renewable energy, such as offshore wind energy, is one approach to reducing anthropogenic carbon dioxide (CO 2 ) emissions by providing alternatives to the combustion of fossil fuels. Many scientists concur that renewable power is important for addressing climate change and reducing its longer term environmental impacts (see text box "Effects of Climate Change on the Ocean"). 1 As interest in the potential benefits of harnessing offshore wind for energy grows in the United States, some stakeholders have expressed concerns about the impacts that offshore wind energy development may have on the marine ecosystem and associated species. Environmental impact statements (EISs) for proposed offshore wind projects have found a range of impacts—both adverse and beneficial—on various resources; these impacts are mostly projected to be minor to moderate, while in some cases they are negligible or major. 2

As the federal government pursues policies for the development of offshore wind energy projects on the U.S. outer continental shelf (OCS), 3 Congress may continue to deliberate actions to mitigate the potential effects of offshore wind energy projects (across several developmental stages) on the marine ecosystem and associated species. For example, the James M. Inhofe National Defense Authorization Act for Fiscal Year 2023 (Division J, Title CXIII, Subtitle C, §11319, of P.L. 117-263 ) directed a study of the impacts on certain marine living resources from the development of renewable energy on the West Coast. In the 118 th Congress, House-passed legislation would direct the Government Accountability Office (GAO) to "assess the sufficiency of the environmental review processes for offshore wind projects," including offshore wind impacts on finfish, invertebrates, whales, and other marine mammals. 4

This report discusses various aspects of how offshore wind projects may impact the marine ecosystem and associated species. First, the report discusses impacts that may be associated with different offshore wind project activities (e.g., site assessment and construction). Second, the report discusses how offshore wind projects may alter the local ocean environment and the ways in which certain species may be directly or indirectly impacted by offshore wind projects. The report in part draws on observational studies of ecological impacts surrounding offshore wind farms (OWFs) in the North Sea, since this area of the world provides the longest record of modern OWFs (see " U.S. Offshore Wind Energy in a Global Context ," below). Other potential species impacts are informed by observational studies of land-based wind farms (e.g., collision risk to birds) or laboratory studies mimicking conditions (e.g., noise levels) often associated with offshore wind construction or operation. Third, the report discusses the responsibilities of federal agencies under various laws to consider and potentially mitigate these impacts. The broader role of federal agencies in the development of offshore wind (beyond environmental review) is outside the scope of this report. 5 Finally, the report discusses some issues for possible congressional consideration, such as additional research on potential impacts associated with offshore wind on the U.S. OCS and competing ocean uses.

Compared with some European and Asian countries, the United States' deployment of offshore wind energy on the U.S. OCS is at an initial stage. 6 Some countries began exploring the development and deployment of modern OWFs as early as the 1990s, when Denmark, the United Kingdom, Sweden, and the Netherlands built OWFs as demonstration projects in the North Sea. 7 In 2022, Europe accounted for 51.0% of global offshore wind capacity, followed by Asia (48.9%). 8 China's offshore wind experienced substantial growth in 2021 and 2022; by the end of 2022, China accounted for nearly 44% of the world's offshore wind capacity. 9

According to the Department of Energy, the United States has 59 offshore wind projects in federal and state waters at various stages of development, ranging from conception to construction to fully commissioned. 10 In federal waters, the Department of the Interior's (DOI's) Bureau of Ocean Energy Management (BOEM) has issued more than 30 leases for offshore wind development (some covering multiple projects) and anticipates completing review of at least 16 construction and operations plans (COPs) by 2025. 11 Several projects are currently operating in state and federal waters in the Atlantic region. 12

Several executive branch and congressional actions have set the stage for increased development and deployment of offshore wind energy on the U.S. OCS. 13 For example, Section 388 of the Energy Policy Act of 2005 ( P.L. 109-58 ) amended the Outer Continental Shelf Lands Act (43 U.S.C. §§1331-1356c) to authorize the Secretary of the Interior to offer leases, easements, and rights-of-way for offshore renewable energy activities on the U.S. OCS. 14 BOEM is the lead agency for the U.S. OCS renewable energy leasing program. 15 In the 117 th Congress, Section 50251 of the Inflation Reduction Act of 2022 ( P.L. 117-196 ) expanded BOEM's authority to pursue offshore wind leasing in federal waters in the southeastern Atlantic region, in the eastern Gulf of Mexico, and off U.S. territories. 16

On the executive side, the Biden Administration suggested a doubling of offshore wind by 2030 as one potential approach to address climate change in Executive Order (E.O.) 14008, "Tackling the Climate Crisis at Home and Abroad." 17 In March 2021, the Biden Administration announced a government-wide effort to deploy 30 gigawatts (or 30,000 megawatts) of offshore wind energy by 2030. 18 In September 2022, the Administration announced a related goal to deploy 15 gigawatts (or 15,000 megawatts) of installed floating offshore wind (i.e., structures that are not set into the ocean floor) by 2035. 19 As of December 2023, BOEM has conducted 12 competitive wind energy lease sales for areas on the OCS, representing more than 2.5 million acres of commercial wind energy lease areas offshore of Delaware, Louisiana, Maryland, Massachusetts, New Jersey, New York, North Carolina, Rhode Island, South Carolina, Virginia, and California. 20

Stakeholders have expressed concerns regarding potential impacts to the marine ecosystem and associated species that pertain to offshore wind project activities associated with site development, construction, operation, and decommissioning. 21 The following sections provide background on offshore wind energy turbine structures and discuss activities associated with offshore wind projects, including the potential impacts of these activities on the marine ecosystem and species.