Grade 3 students were asked to solve a sedimentation problem in a local river. With scientists, students explored many aspects of the problem and proposed solutions. Graphic representation tools were used to help students to better pose the problem. Using questionnaires and interviews, researchers observed students' capacity to pose the problem and their solutions before and after the use of the representation tools. Even if environmental problems are complex and ill-structured, the young students made progress toward more coherent representations and better solutions. Representation and problem-solving strategies to improve children's capacity to better pose a problem are suggested. (Contains 1 table and 2 figures.)