Streamwater gains and losses to and from groundwater impact stream hydrology, solute transport, and biogeochemistry. Most streams are both losing and gaining water across a given reach. The balance of these gains and losses results in a net change in discharge across the reach. Landscape position, topography, fluvial system morphology, and groundwater connectivity can partially control stream gains and losses. We performed stream tracer injection experiments across the Bull Trout watershed stream network, Sawtooth Mountains, ID to investigate stream hydrologic and biogeochemical dynamics and their relationship to landscape position. Our results indicated that stream gains/losses vary widely across the landscape. Gross gains varied from 2-85% and gross losses varied from 4-75% relative to discharge at the upstream end of the reach. These results suggest that stream gains/losses cause considerable turnover of stream water on our experimental time scale (<6 hr), impacting in-stream nutrient uptake and solute transport. Accounting for these dynamic gains and losses across stream reaches may be necessary for accurate depiction of reach hydrologic, solute transport, and biogeochemical dynamics.