Decadal warming has intensified Microcystis-dominated cyanobacterial blooms in Lake Erie

Cyanobacterial harmful algal blooms (CHABs) are increasingly common in freshwater ecosystems and are often associated with climate change. Here, we used two independent high-resolution surface temperature records (1995–2022) and temperature-dependent growth rates of Microcystis to evaluate changes in these CHABs in Lake Erie. The potential mean seasonal growth rate of Microcystis and the duration of the Microcystis bloom season have both significantly increased within the western basin of Lake Erie since 1995. Trends were strongest in the far western region of Lake Erie including Maumee Bay which receives the largest point source of nutrients in the Lake and where the Microcystis bloom season has expanded by up to 1 month. In contrast, warming trends in bloom-free portions of central and eastern Lake Erie have been more muted. We conclude that increasing water temperature is an important factor facilitating the intensification of these, and likely other, CHABs, and is thus promoting an expanding public health threat.