Algal blooms in freshwater ecosystems degrade critical ecosystem services provided by rivers, streams, and lakes, such as habitats that sustain biodiversity, irrigation and drinking water, and areas of significant cultural and recreational value. While planktonic algal blooms have been a major environmental issue studied in lakes, estuaries, and oceans for decades, algal blooms in rivers have only recently become an emergent environmental issue of broad scientific and management concern. Yet the meaning of the phrase “harmful algal bloom” in a river is often indistinct, making management and research priorities on this topic unclear. The complexity of river networks, which can include shallow waters, impoundments, and flow modifications, results in diverse bloom-like phenomena depending on the specific characteristics of sites within the network. In this talk, we define key types of algal blooms in rivers and discuss their differences and similarities, including benthic toxin-producing (i.e., harmful) cyanobacterial mats, nuisance benthic filamentous algal blooms, and planktonic blooms, either originating from within rivers or upstream lentic water bodies (i.e., reservoirs or lakes). Impacts from these different types of bloom events are on a spectrum from nuisance to harmful. We draw on recent literature to evaluate the potential of different tools to detect, quantify, predict, and manage these diverse bloom types (e.g., remote sensing, in-situ sensors). Finally, we outline key research priorities to better understand and predict the spatial extent, temporal dynamics, and ecological consequences of algal blooms in rivers.