Decision making for complex issues like flooding requires critical evaluation of evidence and synthesis of scientific knowledge across disciplines, in particular determining whether flooding is increasing in terms of both frequency and intensity, as well as discerning the underlying causes. This holds significance because students represent the future leaders and decision-makers of society. An understanding and appraisal of the evidence concerning the changing pattern of flooding phenomena worldwide due to climate change will enrich perspectives and influence societal decision-making in future. Our aim was to investigate how students find, analyze, and interpret evidence pertaining to the issue of flooding from online sources. The study was conducted in a post-secondary, large-enrollment, science-literacy course that uses structured decision-making to guide students in evaluating multiple alternative solutions to an SSI (e.g., flood mitigation policies) to reach a conclusion. Students initially learned about floods and their changing pattern around the world. Following this, they were asked to express their understanding of whether flood events were becoming more extreme, evaluate evidence related to flooding, and provide reasoning in support of their ideas. Analysis indicates that 73% of students thought floods were becoming more extreme, and 47% included climate change in their explanation of 'Why?' When asked to find a source of evidence online to support their reasoning, only 13% of students found peer-reviewed sources and 90% of students correctly interpreted the evidence. Most students (82%) found agreement between their initial idea about flood and online evidence. These findings will improve understanding of how students find and integrate evidence in their reasoning about complex issues like flooding and will also inform instructors as they connect disciplinary learning to real-world issues which students care about to enhance their motivation and interest in STEM.