The annual runoff is extremely variable with the possibility of no flow occurring due to a weak snow pack or lack of summer rain. Monthly average flows in the springtime average several hundred cfs and can reach 2,000 to 3,000 cubic feet per second. Only the upper reaches of the river above St. Johns, and the lowermost stretch below Cameron, flow year round; the middle section is basically a huge arroyo that carries water only during the wet seasons.