Broadening participation of diverse groups in Science, Math, Engineering and Technology (STEM) fields is critical to future science success. The goal of the MH-YES project is to engage a diverse group of local high school students in authentic water quality research experiences to build their knowledge, skills, motivation, and confidence for pursuing environmental science. Students did collaborative research into human influences on the ecology of the Fall Kill. Research teams, each comprising three high school students, a mentor scientist, an undergraduate student and a high school science teacher, worked out of two institutions in the Hudson Valley: Cary Institute of Ecosystem Studies and Marist College. Over six weeks, MH-YES teams gained insights into factors that influence two important types of contamination in the Fall Kill: Fecal Indicator Bacteria (FIB) and road salt. The Marist College team evaluated FIB abundance on two types of riparian plants at three sites along the Fall Kill, and the Cary Institute team studied salt retention in different soil types along the Fall Kill and how road salt runoff influences grass seed germination. They also participated in science-identity-supporting activities, such as a panel discussion on diversity in science, a workshop on science communication, and many others.