Back in the day, it was common practice to dump everything in the river. The by-product is "coal tar". The recent re-development of Confluence Park in Denver (the South Platte river and Cherry Creek) was delayed for a year when coal tar was discovered during construction near REI (the former powerhouse for the entire Denver trolley system).
They are just now beginning the abatement process to remove it from the river. Of course, the project will not be coming in under budget. Lol