In 1969 the shock of the Cuyahoga River (among others) bursting into flames prompted passage of the Clean Water Act. But even in that era of political will, agriculture was given a pass; chemical fertilizers were crucial to the industrial farming needed to feed the growing human population, so their usage wasn’t regulated. As Egan shows in this urgent account of our relationship with phosphorus, this lapse set in motion some of today’s most intransigent problems, notably the growing size and numbers of toxic algae blooms, whose thick waves of cyanobacteria close beaches and fisheries around the country. Yet even as marine life continues to die and humans to sicken, phosphate levels keep rising. To understand the problem, Egan takes us on a fast-paced tour of the confounding nature of this “devil’s element,” tracing its role as both a toxin and a crucial element in the evolution and sustenance of earthly life, a nonrenewable resource vulnerable to ruinous exploitation, a World War I weapon, whitener in laundry detergent, and more.