Invasive species pose a serious risk to ecosystem health and stability around the world and locally. Why should we be concerned about invasive species? How do they change local plant and animal communities? How do they change the chemistry of a water body like the Hudson River? Students will learn how and why invasive species have such large ecosystem impacts and how they have changed the Hudson River. This unit includes a more in-depth investigation of three species: zebra mussels, water chestnut, and common reed. As students will discover, all of these introduced species have changed the ecosystems around us in potentially positive and negative ways. The concluding research report provides an opportunity for students to explore other local invasive species.