Development of the marine renewable energy (MRE) industry has been challenged by uncertainty about potential environmental effects, which has resulted in slowing of permitting/consenting processes, and ultimately to constraints on the industry. These challenges result from a lack of sufficient devices in the water from which to learn, a dearth of quality monitoring data, and a lack of accessibility to information about these effects in general. This paper describes an ongoing process to improve understanding of the environmental effects of MRE through a public, online knowledge management system developed by the U.S. Department of Energy, known as Tethys (https://tethys.pnnl.gov). Tethys collects and curates relevant documents while supporting a diverse international community through intentional outreach and synthesis activities, many of which support an international collaboration under the IEA Ocean Energy System’s Annex IV. After eight years of operation, Tethys is internationally recognized and viewed as a trusted broker of information, with over 50,000 visitors annually. Tethys has provided clarity around environmental effects during a critical time in the industry when deployments are increasing in size and frequency.