The internationalisation of higher education as well as the emergence of evidence for the claim that bi/multilingualism in science should be the norm, not just an option, are conditions that explain the rise in university bilingual science courses. Thus far, however, little is known about how to foster bilingual scientific argumentation in this type of course. The purpose of this study was to provide evidence that the creation of bilingual scientific argument podcasts (BSAP) -- a form of podcast where two languages are used to communicate elements of scientific argument structure (e.g. argument, counterargument, rebuttal) -- can be used as a springboard to foster undergraduate bilingual scientific argumentation. The data was derived from scripts of the podcast episodes produced by twenty-seven students (19 females and 8 males, 19-25 years old) during a university Spanish-English bilingual science course taught within a formative assessment environment. Results indicate that student-created BSAP effectively enriched participants' skills to produce (counter) arguments and rebuttals in Spanish (g = 0.79) and in English (g = 1.20). Moreover, findings suggest that undergraduates benefited from formative assessment practices such as instructor feedback and peer feedback. Implications related to bilingual science education practices and supporting students' development of bilingual scientific argumentation within formative assessment environments are discussed.