This is an activity I use as a visual for the students to see the different types of pollution that affect rivers. I modify it by talking about the MO river.
One of my foundational rules of classroom engagement is simply this: never be the first one to open your mouth and start talking about any topic. Twenty years in the classroom taught me that one. Never assume. Never take prior knowledge for granted. Listen first, then act. Never presume to know what the students in front of you are capable of. They'll show you if you are bold enough to listen.