S. 3743 directs the Secretary of the Interior, through the Bureau of Reclamation, to study ways to address invasive fish species below Glen Canyon Dam while also protecting hydropower production. Working with the Department of Energy, the Fish and Wildlife Service, the Geological Survey, Colorado River Basin states, and power contractors, the Secretary must evaluate infrastructure options such as a thermal curtain or a selective water withdrawal system that would allow cold water releases to control invasive species without harming power generation. If an alternative is found feasible, the Secretary may move forward with design and construction. The study must be completed within 18 months, with a detailed report—including cost estimates, effects on hydropower rates, and a formal recommendation—submitted to Congress within 90 days after that. The bill directs Interior to identify funding sources within 90 days of enactment, clarifies that this effort does not change existing Colorado River reservoir operating rules, and sets the authority to expire five years after enactment. This measure primarily affects water and power management in the Colorado River Basin, including hydropower customers, downstream ecosystems, and the states and tribes that rely on the river system.