Cyanobacteria produce toxic/bioactive metabolites that affect human and ecosystem health via inhibition of proteases, carboxypeptidases, or phosphatases. From surface water samples collected between 2016 and 2019 inclusive (n = 78), we report intracellular concentrations of more than 30 such compounds in Lake of the Woods (LOW), a large lake system of multinational importance. Although most surface bio-mass blooms were dominated by the cyanobacteria Dolichospermum (max.-50 mg/L) and Aphanizomenon (max.-60 mg/L), there was also significant biomass of other cyanobacteria (Gloeotrichia echinulate along shoreline, max.-40,000 mg/L; Woronichinia naegeliana max.-100 mg/L; Lyngbya max. -10 mg/L; Planktothrix agardhii max. -6 mg/L) and phytoplankton (Stephanodiscus niagarae max.-6 mg/L). Microcystins (MCs) were present in-80 % of samples, peaking at-33 mu g/L (MC variant-LR). Approximately 50 % of samples contained MC concentrations below 0.1 mu g/L. Alkaloid metabolites detected included neurotoxin anatoxin-a (-60 % < 0.1 mu g/L) and cytotoxic cylindrospermopsins (-30 % < 0.1 mu g/L). Anabaenopeptins A/B/F were prevalent (>96 %) and exceeded MCs by >100 fold (max. >4,000 mu g/L). Aeruginosamide B was present in-75 % of samples (max.-10 mu g/L). Cyanopeptolin 1040 MB, microginin 690 methyl ester, and oscillaginin A were not detected however, traces of micropep-tin 1106 were detected. Microcystin and anabaenopeptin genes were also detected in the majority of samples (78 % and 79 %, respectively), while saxitoxin, cylindrospermopsin, and anatoxin genes occurred at lower frequencies with 59 %, 36 %, and 38 % detection, respectively. These results will aid assessment of risk from cyanobacterial blooms in LOW and inform ongoing binational lake management and policy development. CrownCopyright (c) 2022 Published by Elsevier B.V. on behalf of International Association for Great Lakes Research. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).
