The Oahu watershed (HUC 20060000) covers an area of approximately 588 square miles and is located entirely on the island of Oahu in Hawaii. The hydrology of the watershed is characterized by a combination of surface water and groundwater resources. The snowpack is not relevant to this region as it does not experience snowfall. Surface water quality in the watershed is heavily influenced by human activities, including urban development, agriculture, and industrial activities. The primary reservoir in the watershed is the Wahiawa Reservoir, which serves as a domestic water supply for the island. Interesting climatic facts include the frequent occurrence of trade winds, which bring cool air and rain to the island, and an increasing trend in the frequency and severity of extreme weather events, such as hurricanes and floods, in recent years.