## 1 Introduction  
Cyanobacterial harmful algal blooms (cyanoHABs) are increasing in frequency, duration, scale, and severity in freshwater systems across the globe, and their adverse ecological and human health impacts are predicted to be exacerbated by the impacts of climate change [1,2]. CyanoHABs are caused by cyanobacteria that proliferate under favorable nutrient, water temperature, weather, and light conditions to form areas of high cell density that often release potent cyanotoxins, rendering water bodies unusable and potentially hazardous [1,3,4]. Numerous remediation strategies exist for cyanoHABs, including mechanical harvesting (i.e., physical removal of floating cyanobacteria), reduction in nutrients such as phosphorus through the use of sorbents or dredging, ultrasonic treatment to impair cell buoyancy, application of biocontrol/biomanipulation agents to stimulate growth of species competitive with or predatory to cyanobacteria (e.g., macrophytes and zooplankton), and application of chemical algicides and cyanocides (e.g., copper and aluminum salts), oxidants (e.g., hydrogen peroxide), and coagulants/floculants (e.g., polyaluminum chloride and chitosan) [3,5]. Each of these remediation strategies has unique benefits and limitations; however, the two shortcomings consistent across all of the strategies are scalability and adverse off-target effects on the surrounding ecosystem due to imprecise, wide-area application [6]. One treatment technology that has shown promise in suppressing cyanoHABs in both laboratory and field studies and may face fewer obstacles to achieve scalability and ensure limited off-target ecological effects in the surrounding area is irradiation of cyanobacteria with germicidal ultraviolet light (UV-C). Disinfection of water using UV-C is ubiquitous at drinking water and wastewater facilities across the United States and has demonstrated high efficacy in protecting human health through the inactivation of harmful pathogens [7,8]. The U.S. Environmental Protection Agency (EPA) (1999) states that UV disinfection is effective at inactivating most viruses, spores, and cysts, and that it has a shorter contact time when compared with other disinfectants. Additionally, there is no residual effect that can be harmful to humans or aquatic life [9]. UV-C has also been used in surface waters as a chemical-free biocide/herbicide to suppress the growth of unwanted flora and fauna for decades without introducing potentially harmful chemicals into the ecosystem [10]. For example, in situ exposure of certain submerged aquatic vegetation (SAV) to UV-C has been shown to significantly reduce plant biomass and height. In a field study, [PERSON] et al. (2022) reported a 100% reduction in biomass (complete eradication) of invasive curly leaf pondweed (_Potamogeton crispus_) after in situ irradiation with germicidal UV-C, and found mature plants were the most vulnerable/susceptible life stage to germicidal UV-C, with observed loss of turgor pressure and chlorophyll _a_[11]. Similarly, a pilot study conducted by the Lake Tahoe Resource Conservation District, in which a boat equipped with a UV-C lamp array (not contained within a reactor) irradiated various SAV species in both an enclosed waterbody (i.e., marinas) and open waterbody (i.e., beach littoral zone), showed that the application of UV-C results in mortality of SAV, and most macrophytes (macroophytes in the study included Eurasian watermilfoil (_Myriophyllum spicatum_), curly leaf pondweed (_Potamogeton crispus_), Richardson's pondweed (_Potamogeton richandsoiii_), Leafy pondweed (_Potamogeton foliosus_), Coontail (_Centaphyllum denersum_), _Eladen_ spp., and Sago pondweed (_Stuckenia pectinate_) treated with UV-C exhibited signs of deterioration within 7 to 10 days following treatment [12].