Lake Superior has recently begun experiencing cyanobacterial blooms comprised of Dolichospermum lemmermannii near the Apostle Islands and along the southern shore of the western arm. Little is known about the origin of these blooms. Experiments were conducted during the summers of 2017 and 2018 to identify sources of propagules and characteristics of sites that were potential sources. The 2017 experiments were conducted using a factorial design with three source zones (‘River’, ‘Lake’, and ‘Harbor’), two nutrient conditions (high and low N:P), and three temperatures (15, 20, and 25°C). At the end of the experiment, cyanobacteria were most abundant from the ‘River’ and ‘Harbor’ zones at low N:P and 20 and 25°C, with D. lemmermannii most abundant at 20°C. Subsequently, in 2018 we evaluated 26 specific inland locations from three waterbody types (‘River’, ‘Lake/Pond’, and ‘Coastal’) and explored similarities among those sites that produced cyanobacteria in high abundance when samples were incubated under optimal conditions (low N:P and 25°C). Under these growing conditions, we found high cyanobacteria abundance developed in samples from river sites with low ambient temperatures and high conductivity. Field monitoring showed that Lake Superior nearshore temperatures were higher than rivers. These observations suggest that blooms of D. lemmermannii in Lake Superior are initiated by fluvial seeding of propagules and highlight the importance of warmer temperatures and favorable nutrient and light conditions for subsequent extensive cyanobacterial growth. We argue that the watershed is an important source of biological loading of D. lemmermannii to Lake Superior and that when those cells reach the nearshore where there are warmer water temperatures and increased light, they can grow in abundance to produce blooms.

苏必利尔湖最近开始在使徒群岛附近和西海岸的南岸经历蓝藻水华，其中包括Dolichospermum lemmermannii。这些花的起源知之甚少。在2017年和2018年夏季进行了实验，以确定繁殖物的来源和潜在来源的特征。2017年的实验是采用因子设计进行的，其中包括三个源区（``河''，``湖''和``港口''），两个营养条件（高和低N：P）以及三个温度（15、20和25） °C）。在实验结束时，蓝细菌在蓝皮病菌（D. lemmermannii）中处于低N：P且温度为20和25°C时，来自“河”和“港”区最为丰富。在20°C时最丰富。随后，在2018年，我们从三种水体类型（``河流''，``湖泊/池塘''和``沿海''）评估了26个特定的内陆位置，并探索了在最佳条件下孵育样品时产生大量蓝藻的站点之间的相似性（低N：P和25°C）。在这些生长条件下，我们发现在环境温度低和电导率高的河流地区的样品中产生了很高的蓝细菌含量。现场监测表明，苏必利尔湖近岸温度高于河流。这些观察结果表明莱姆曼氏小球藻的开花苏必利尔湖的繁殖源是通过繁育繁殖体而开始的，突出了温度升高，有利的养分和光照条件对于随后广泛的蓝藻生长的重要性。我们认为，分水岭是蓝默氏梭菌到苏必利尔湖的生物负载的重要来源，当这些细胞到达近岸时，那里的水温升高且光线增加，它们可以大量繁殖以产生花朵。