The complex environmental challenges humanity faces require citizens who are scientifically and environmentally literate. Many environmental education programs are situated in the field where students are immersed in their learning. These field-based activities are engaging but may lack opportunities for students to develop critical thinking and reasoning skills necessary to be environmentally literate. We suggest a socio-scientific issue (SSI) based teaching approach can increase epistemic engagement and lead to student gains in scientific and environmental literacy. This study describes how we modified an existing field-based ecology course, framing the learning around a local environmental socio-scientific issue. We used a convergent parallel mixed-methods approach to examine the changes in socio-scientific reasoning (SSR) over time for high school students in this course as a measure of scientific and environmental literacy. Results indicate that a focused SSI field-based environmental education curriculum can support development of socio-scientific reasoning and environmental literacy competencies among high school students.