The image is a diagram illustrating the concept of a dam and its impact on water levels. The diagram shows a dam with two sections: the upper section labeled "Ocean" and the lower section labeled "Lock." The upper section is connected to the ocean, while the lower section is connected to Gatun Lake. The dam is depicted as a rectangular structure with a lock at its base, which allows water to flow through it. The diagram highlights the difference in water levels before and after the dam's construction, demonstrating how the dam has altered the flow of water.