This Guidance Document on Conducting Studies of Selenium in Fish Tissue was developed by MAC to support companies required to conduct such studies under the Metal and Diamond Mining Effluent Regulations (MDMER). The guidance document has been developed taking into account the MDMER requirements for Environmental Effects Monitoring (EEM), best practices and the state-of-the-science related to selenium in fish tissue. The document provides fit “for purpose guidance” for the conduct of MDMER studies of selenium in fish tissue, helping to ensure that collection of high-quality data. The guidance is intended to be used in conjunction with guidance prepared by Environment Canada for conducting EEM studies: Metal Mining Technical Guidance for Environmental Effects Monitoring.