Why do the gamemakers dry up the river and ponds?

In "The Hunger Games," the Gamemakers dry up the river and ponds to create a more challenging and dangerous environment for the tributes. This manipulation heightens the stakes and forces the participants to compete for limited resources, increasing the tension and drama of the Games. By controlling the natural elements, the Gamemakers can steer the narrative and influence the tributes' actions, making the event more entertaining for the Capitol audience.