As the world’s largest dam removal began in the Klamath River in January 2024, fisheries managers were concerned that dissolved oxygen would fall below lethal levels during and after the drawdown of the associated reservoirs. The initiation of drawdown at the two farthest dams downstream, Copco II and Iron Gate Dams, resulted in a substantial amount of suspended sediment, rich with organic carbon from a century of cyanobacteria blooms, released downstream into the mainstem Klamath River. Associated with these releases were pulses of anoxic hypolimnetic water from the reservoirs. These events were accompanied by two sags in dissolved oxygen to levels considered fatal to the at-risk fish, such as Pacific salmon (Oncorhynchus spp.) and Green sturgeon (Acipenser medirostris), that are native to the Klamath River. The primary objectives of this study were to measure the magnitude and duration of dissolved oxygen sags during the dam removal, identify the mechanisms that contributed most to these sags, and assess whether these dynamics changed with distance downstream. Dissolved oxygen, streamflow, turbidity, and water temperature were monitored for two months prior to and four months after initiation of drawdown at three sites located downstream of the lowest dam. Sediment and water samples were collected weekly at these three sites to evaluate the relationships between particulate and dissolved organic carbon and biochemical oxygen demand in a controlled laboratory setting. The study documented four distinct dissolved oxygen sags during the drawdown process - two of which were to lethal levels. These sags were associated with rises in turbidity, particulate organic matter, and oxygen consumption rate. Data from closed incubations suggest at least two distinct processes consuming dissolved oxygen at different time scales during the sediment pulses. These data provide important insights into mechanisms driving dissolved oxygen dynamics that can inform future river restoration efforts.