In-stream tidal energy initiatives are rapidly developing in Nova Scotia, Canada, but there remains a high degree of uncertainty regarding the nature and extent (in space and time) of environmental implications of energy harvesting activities. To ensure the tidal energy industry in Nova Scotia (and elsewhere in Canada) develops in an environmentally safe and sustainable manner, regulators and industry are in need of a consistent, objective and efficient approach to assess and mitigate the risk of adverse environmental impacts of a proposed project. This paper presents a science-based environmental risk assessment and decision-making framework developed on behalf of the Nova Scotia Department of Energy and Fisheries and Oceans Canada (Federal). The framework offers key steps and considerations for identifying, assessing, and addressing the environmental risk of in-stream tidal energy projects based on the best available scientific knowledge, expert advice, and best practices for environmental risk and impact assessment. The risk assessment approach is based on a set of practical criteria and related risk indictors that are relevant, flexible and can be consistently applied to projects of any type, size or location. By following this approach, project planners and reviewers can also gain insights as to: site-appropriate project design and size consideration; the level and type of baseline studies and monitoring that may be required; methods of mitigating or reducing the level of risk of a project; and evaluation measures or trigger points for adaptive management actions. The guidance framework has been peer reviewed by scientists, industry and provincial and federal government agencies and is intended to form the basis of a joint Canada/Nova Scotia Statement of Best Practice for the management of in-stream tidal energy development.