A red tide is a natural phenomenon that develops miles offshore before making its way to the coast, where it feeds on a variety of pollutants, including phosphorus and nitrogen from fertilizer, along with other runoff and wastewater. The toxins can aerosolize in the wind that drifts ashore, triggering respiratory problems or worsening conditions such as asthma.

What is not clear is whether climate change and pollution from humans near the shore has made this outbreak severe and prolonged. Scientists have found that the algae thrive in warmer waters and increased carbon dioxide levels.