Flow is the volume of water moving past a point in a unit of time. Two things make up flow: the volume of water in the stream, and the velocity of the water moving past a given point. Flow affects the concentration of dissolved oxygen, natural substances, and pollutants in a water body. Flow is measured in units of cubic feet per second (cfs). Peak flows for Boulder Creek in the spring can reach as high as 300-800 cfs and as low as 10-50 cfs in the fall months.