This article showcases STEM as an interdisciplinary field in which the disciplines strengthen and support each other (not as separate science, technology, engineering, and mathematics disciplines). The authors focus on an open-ended, complex problem--water quality--as the primary teaching and learning task. The participants, middle school female students (aged 9-15 years), interacted in an informal educational setting (i.e., Girl Scouts) on a research project investigating river quality following the river's restoration. The community, including Girl Scout participants, leaders, parents, university faculty, graduate students, and others, utilized an action research (AR) approach when interacting with the participants. Methods such as observational field notes, focus groups, and collected artifacts were commonly employed. The authors describe the history of STEM and AR leading to authentic science research projects through eight engineering skills/practices (incorporating science, technology, and mathematics) and showcase participant interactions, implementation, and community engagement in the STEM water quality river project. Findings indicate that informal engineering based projects can serve as opportunities for participants to connect with integrated STEM. Implications include the need for engaging participants in informal authentic science to support traditional school STEM learning and encouraging community engagement in integrated STEM to support traditional K-12 classroom instruction.