That's right, dinoflagellates

I was in New England. Off the coast, on a rowboat, I smelled something strange, metallic, and acrid. I soon heard that the same smell was reported in the Midwest, off the shores of the Great Lakes, and was spreading. I figured that the smell was some sort of sensory horseman of the apocalypse, but then the official report came out. The coastal and lake waters had experienced unusual red tides containing dinoflagellates, which gave off toxins that caused the smell.