The Earth’s carbonate-silicate cycle is an important regulator of atmospheric carbon dioxide, which has stabilized Earth’s climate over geologic time. New geoengineering approaches aim to enhance the rate of silicate rock weathering by mining, milling and distributing silicate minerals on land to facilitate heightened rates of CO2 consumption in weathering reactions. In order to be effective as a climate mitigation approach, the bicarbonate ions and cations produced by enhanced rock weathering (ERW) must ultimately be transported to the deep ocean. While a great deal of recent research has focused on the efficacy of this geoengineering approach on land, far less attention has been paid to the fate, transport and impact of these ERW solutes as they are routed through freshwater ecosystems. Here we attempt to synthesize what is already known about the fate, transport and impact of bicarbonate and cations in rivers and suggests priorities for the freshwater science community for helping maximize the efficacy and minimize the unintended consequences of this important new climate mitigation strategy.