context: Lighthouses dams are skillful structures made of wood, rocks, mud, knots and other similar needs. The beaver usually does construction work in the mornings, after dining in the evening. The dam is built upstream downstream so that a beaver pushes the construction tree dam into a suitable gap and is pressed firmly into the dam. The first dam trees are sloping downstream. Thinner branches and twigs form spacings of thick trees, as do stonework. The dam is covered with mud, twigs and pebbles. The bark of trees used for dams is usually eaten before construction. If the water rises above the dam, it will be raised or extended to the side. More than three meters of dams have been found and they have been claimed to be up to a kilometer wide. The purpose of the dam is to raise the water surface of the body of water so that the beach tree can be more easily reached by the beaver, while keeping the mouth of the nest below the water level. [11]
question: Why do beavers build dams?
answers.text: The purpose of the dam is to raise the water surface of the body of water