Beach Act of 2017 This bill amends the Federal Water Pollution Control Act (commonly known as the Clean Water Act) to revise and reauthorize through FY2021 a grant program for monitoring, and notifying the public of, any pathogens in coastal recreation waters bordering public beaches. The bill reauthorizes through FY2021 the Beaches Environmental Assessment and Coastal Health Act of 2000. The bill establishes requirements with respect to: (1) using rapid testing methods to detect unsafe levels of pathogens or pathogen indicators in such coastal recreation waters, and (2) notifying governmental agencies when pathogens exceed water quality standards. Those methods must provide testing results within four hours of receiving a sample. The applicable state or local government must communicate the presence of any pathogens within two hours of receipt of a water quality sample. The Environmental Protection Agency (EPA) must assess state and local compliance with coastal recreation water quality monitoring and notification legal requirements and grant conditions. The bill limits federal share of grants to non-compliant state or local governments. The Government Accountability Office must review the EPA's compliance assessments and corrective actions. States with coastal recreation waters must adopt the most protective water quality criteria and standards practicable for pathogens. The EPA must: (1) update the national list of beaches that are used by the public regardless of the presence of a lifeguard within 12 months and biennially thereafter (currently, periodically); (2) study the long-term impact of climate change on pathogenic contamination of coastal recreation waters; and (3) study the impacts of excess nutrients on coastal recreation waters.