The river running through Cleveland used to be so polluted that it caught fire at least a dozen times.[1]
[1] https://www.smithsonianmag.com/history/cuyahoga-river-caught...
[1] https://www.smithsonianmag.com/history/cuyahoga-river-caught...
https://discworld.fandom.com/wiki/Great_Fire_of_Ankh-Morpork