beaver dams smooth out water flow by increasing the area wetted by the stream. This allows more water to seep into the ground where its flow is slowed. This water eventually finds its way back to the stream. Rivers with beaver dams in their head waters have lower high water and higher low water levels.
They might be going through the S Phase of the cell cycle which is DNA replication. Usually, when the cells go through this phase they end up to dividing.
