Cut up the egg carton and secure each piece with glue to your cardboard base. Use each individual piece of the egg carton to form the structural elements of a steep mountain.

Mix your wallpaper paste with water until it becomes runny. Cut up your newspaper into 1-inch strips, dip them into your water/wallpaper paste mixture and paste the strips over the egg carton pieces. Add several layers of newspaper, allowing each layer to dry before adding the additional layer, until you make a mountain that is steep in one area then finishes in a flat area.

Allow your project to dry, which could take about 12 to 24 hours.

Paint your river basin project to look like a river basin. Use gray and white paint on the mountain, green and brown paint on the land and blue paint for the water. There will be a lake at the base of the mountain, and a river running along the middle of the project into the lake.

Show the watershed using a piece of string secured to the project with glue. The string runs along the edges of the project to indicate areas where the water drains into your river.

Build small flags using cocktail sticks and paper. You can use these flags to label areas of your river basin project, such as the tributary, confluence, estuary and lake. Secure your flags to your project with glue.