Rivers gain water from groundwater, in this case, a nearby geyser

Groundwater contributes to streamflow in most physiographic and climatic settings in the world. Many things, such as a region's geography, geology, soil type and saturation, and climate, determine the proportion of stream water that comes from groundwater. Hydrologists (water scientists) can determine the amount of water that groundwater contributes to streams by analyzing streamflow hydrographs and precipitation records. From these studies, hydrologists can determine how much of a stream's flow comes from runoff and how much comes from groundwater discharging into the streambed.

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