This report provides an overview of the state of affairs (1) with regards to the deployment of wet renewables and (2) marine energy storage systems; (3) how they affect abiotic and biotic components of the marine ecosystem and (4) developments and concepts on cumulative impact assessments related to marine renewable energy devices and (5) future perspectives. This report provides the scientific basis to address the OSPAR request for advice on the current state and knowledge of studies into the deployment and environmental impacts of the following wet renewable energies and marine energy storage (floating, coastal infrastructure), tidal stream (screws, kites), tidal flow (barrage, lagoon) and others. Advice should cover the status of wet renewable developments in the OSPAR region, future prospects, potential environmental prob-lems (sea bed habitat loss/disturbance, fish, marine mammals, birds, seascape/ public perception, and cumulative impacts), potential benefits, next steps and conclusions”. The request was directed towards the Working Group on Marine Benthal Energy Developments (WGMBRED) and the Working Group on Marine Renewable Energy (WGMRE). A pre-meeting chaired by Jan Vanaverbeke, Belgium (WKWET, 15–16 January 2019) at ICES Headquarters, was attended by 11 participants from 4 countries, including members of WGMBRED and WGMRE and additional experts. The group analysed the OSPAR request, agreed on a structure for the report, and certain experts volunteered to conduct a literature re-view and provide the necessary knowledge base for the report.WGMBRED met from 12–15 February 2019 in Brussels, Belgium. The input from WKWET participants was compiled, quality checked and adapted where needed; when relevant expertise was represented in the group. WKWET experts, not present at WGMBRED, reviewed text, where needed, and a first version of this report was delivered to WGMRE.WGMRE met in Oostende (Belgium) from 26–28 February 2019. Participants reviewed the WKWET report following input from WGMBRED, quality checked, and adapted where neces-sary. Relevant experts contributed additional text and data to tables on MRE developments in ICES areas, and provided text on public perceptions and future prospects of MRE. This report presents an overview of the currently known “wet renewables” (all marine renewable energy devices, excluding offshore wind devices) and how their deployment will likely change in the future. It further provides an overview of the concepts and techniques of related to marine energy storage devices. Given the conceptual and experimental stage of marine energy storage devices, and the absence of data on how these devices affect the marine environment, the report is limited to a description of these marine energy storage devices. This report provides a receptor-based summary of how the wet renewables can affect the marine environment. Receptors are either abiotic (hydrodynamics, physical seabed and sediment transport) or biotic (benthos, fish, marine mammals, birds, sea turtles, otters and polar bears). To avoid repetition, effects on these receptors were grouped according to pressure-inducing components (static component of the device, dynamic component of the device, cables) of wet renewables or consequences of their presence. The report further discusses the developments on cumulative impacts assessments associated with wet renewables deployment in addition to many other human activities, and the need to move away from “data rich – information poor” monitoring of structural aspects of the marine ecosystem to hypothesis-driven functional research at the relevant spatial and temporal scales. This will require cross-border coordination in data collection, data storage and exchange and the development of a joint research agenda.