This project will take at least a week before the two formal weeks for prep work.
For the first week, behind the scenes you'll arrange transportation and permission to get the class out to your selected sites. Try to have a pond and a stream location to go to. You may include more than two collecting trips but a great deal can and will be collected at the two sites. Be sure to survey your kids for any allergies or other health issues that need to be addressed.
This first week is good to drum up excitement. I kept a canning jar with collected samples from previous years projects that I passed around and the kids get very curious and excited. However for your first time consider using any of the video or photo links that you may find.
This is also a good time to present the choice of the 3 roles that will be needed and have discussions as to what will be expected for each. Turn over responsibility for choices to the students and express that roles are "dynamic" and can be changed, shared, switched, and modified as long as the final outcome is a quality product that has been developed equitably by the team. Keep in mind that as the Teacher (Executive Director) you may want to assign roles yourself to specific students to meet their individual needs.
The flexibility of using Keynote is that individuals can work separately on slides and then combine them into a single final product. But keep in mind that the overall product should have a common look, theme and style in overall appearance.