Alkalinity refers to how well a water body can neutralize acids. Alkalinity measures the amount of alkaline compounds in water, such as carbonates (CO₃ ^2-), bicarbonates (HCO₃ ^-), and hydroxides (OH^-). These compounds are natural buffers that can remove excess hydrogen ions that have been added from sources such as acid rain or acid mine drainage. Alkalinity mitigates or relieves metals toxicity by using available HCO₃ ^- and CO₃ ^2- to take metals out of solution, thus making it unavailable to fish. Alkalinity is affected by the geology of the watershed; watersheds containing limestone will have a higher alkalinity than watersheds where granite is predominant. The Boulder Creek Watershed is composed primarily of granite rocks, thus the water has a lower alkalinity content.