Cyanobacterial blooms in riverine systems are predicted to increase in frequency and severity worldwide due to changing climate and river regulation. Loads of organic nutrients to freshwater systems are also rising, increasing the potential for harmful blooms further. Yet cyanobacterial blooms can be affected both positively and negatively by the flux, concentration and composition of organic nutrients, as well as being a strong driver of dissolved organic matter (DOM) production and cycling themselves. Here, we: (i) review recent evidence on the effects of DOM on bloom development, duration, and dynamics; (ii) from a landscape perspective, describe how the flux and composition of DOM to lakes, reservoirs, and river channels could be affected by climate change and increasing river regulation; and (iii) predict the combined effects of variation in DOM dynamics and climate change on the frequency and severity of cyanobacterial blooms.