Spring Creek is a southeast-flowing, long tributary of the Sacramento River, receiving water from approximately of land. The creek begins in the Klamath Mountains above the Sacramento River drainage, and flows in a generally south-east direction before turning south and sharply west into the Spring Creek Reservoir. From the reservoir, it continues due west until it empties directly into an arm of the Keswick Reservoir. The creek never actually runs by the mine. The acid mine drainage found in the creek is actually carried in by two smaller tributaries, which are Boulder Creek and Slickrock Creek. The former stream runs southeast from the north side of Iron Mountain Mine to Spring Creek, while the latter stream drains the south side of the mine and also flows southeast into Spring Creek. South Fork Spring Creek is a small tributary that flows west and north the Spring Creek Reservoir, but since its basin lies far from the mine, it receives no acid mine drainage. The inflow and outflow from the reservoir are highly erratic, ranging from per second to roughly per second in a particular 10-day period from March to April.