My Students LOVE this activity. Every year before we start environmental issues we do this activity. I have the students work in groups drawing on a poster board.
You will also need to have black pieces of paper for them to cover up their drawing at the end to simulate pollution. This is editable to change for your own use.
Students will draw a city on a river. Depending on what they draw they will cover their paper with squares that will simulate the pollution everything creates.