America's Water Infrastructure Act of 2020 This bill modifies water resources development projects operated by the Army Corps of Engineers and clean water programs operated by the Environmental Protection Agency (EPA). The bill modifies cost share requirements for the construction and major rehabilitation of certain inland waterways navigation projects. Additionally, the nonfederal cost share for certain projects may be reduced if a small or disadvantaged community's sustainability would be threatened without the project. Similarly, the Corps of Engineers may recommend a project without national economic development benefits if the project is necessary for an underserved, economically distressed, or rural community's sustainability. The Corps of Engineers must also construct small water storage projects in rural states. The bill authorizes new projects, including projects for ecosystem restoration, flood risk management, and navigation. The bill also establishes programs for the prevention and control of certain invasive species. Additionally, the EPA must provide specified assistance to small and medium publicly owned treatment works. Further, the EPA must award grants to small publicly owned treatment works for activities including those related to improving energy and waste efficiency. The EPA must also award grants to reduce emissions at ports from vessels. Further, the bill reauthorizes through FY2024 the Clean Water State Revolving Fund, which provides financing for water quality infrastructure projects. The bill also reauthorizes through FY2030 the Indian Irrigation Fund, which provides funds to maintain and repair Indian irrigation projects. The Government Accountability Office must report on federal dams and reservoirs in western states.