Coal features prominently as cargo barged on America’s Ohio river, where more than 41 dams control the water levels so that barges can move up and down, carrying 150-million tons a year of mainly bulk energy commodities. Seen pushing coal barges upstream in Louisville, Kentucky, is the Janis R Brewer towboat, a 43-m-long, five-year-old tug that navigates the waters of the Ohio, which is said to be the most polluted river in the US.