The famous 1969 Cuyahoga River fire was not a case of water burning, but rather the combustion of a dense, floating layer of industrial pollutants floating atop the water column. For decades, factories, steel mills, and oil refineries along the river in Cleveland discharged untreated industrial waste directly into the waterway. This waste contained heavy concentrations of hydrophobic oily residues, volatile organic compounds, grease, and coal tar derivatives.
Because oil is less dense than water, these non-polar compounds aggregated on the surface, forming a thick, stagnant slick that trapped floating debris such as wooden logs and trash. The ignition process relied on low-flashpoint volatile hydrocarbons trapped within the slick. On June 22, 1969, friction sparks from a passing train on a trestle bridge fell onto the oil-soaked debris floating below.
The sparks raised the local temperature of the volatile light-fraction solvents above their flashpoint, initiating a rapid exothermic reaction. The burning solvents vaporized and ignited the surrounding heavy petroleum slick, sustaining flames that rose over five stories high. The event became a pivotal political catalyst, directly driving the passage of the Clean Water Act of 1972 and the formation of the United States Environmental Protection Agency.