Harmful algae blooms: an analysis of recent spatiotemporal trends on California's inland waterbodies†

Harmful algae blooms (HABs) are unwelcome annual events on waterbodies in California (USA). The unseemly sights of lifeless fish drifting ashore and the mammalian illnesses resulting from close contacts with HABs once in ahile are telltale signs of their presence. California as such tracks HABs closely for immediate public warnings. That said, a lack of statewide monitoring standards for producing comparable and high-quality data, however, hinders a deeper insight into HABs on California's inland waterbodies. In their absence, the current study demonstrates the utility of empirical dataset in advancing an understanding of spatiotemporal distribution of HABs on inland waterbodies. With a 2016–2021 mostly observational data, the questions asked are whether HABs incidences are expanding in California with time, whether there are localities more prone to HABs than others, and whether bivariate relationships exist between HABs reports and population density, or waterbody size, land area and geographical location. Overall, the frequency with which HABs are observed is found to increase statewide, an increase not correlated with population density, but with land area and inland waterbody size. Results also show that North Coast, Central Valley, and San Diego are the most affected regions of California. Also revealed by this mostly observational data were recent HABs spikes in the January months (California winter) which, if proven, may be signaling an emerging year-round problem that California will have to contend with.