generally rural in nature, meandering through game lands, forests, and agricultural properties. The mainstem (lower elevation) flowing mainly southeast extends roughly from Leavittsburg to the river's mouth near New Castle, Pennsylvania. Portions of this section are more densely populated and heavily industrialized, including the cities of Warren, Niles, Youngstown, Campbell, and others. The area suffers with residue from all the industrial activity that began in the late 19th century. The mainstem area has a population of over 500,000 and has a long history of steel making, coke production, and other industries. Environmental concerns The industrial nature of the mainstem area has caused considerable pollution in the river. Much of the pollution has left the ecosystem via the natural river flow. But analysts estimate that 750,000 cubic yards (573,416 m³) of river bed and shoreline sediment, over a 30-mile (48.2 km) stretch of the mainstem from Leavittsburg to the Pennsylvania border, is so heavily polluted that it will need to be remediated. Approximately 45% of this material is located in the vicinity of the Girard Dam near Girard, Ohio, which has acted as a trap for much of the contaminated sediment. Petroleum hydrocarbons, benzo(a)pyrene (polycyclic aromatic hydrocarbons), and mercury have all been found in quantities several times the maximum safe levels. Since 1988, the Ohio Department of Health has maintained an advisory against swimming or wading in the river between Leavittsburg and the Pennsylvania border, and also advises against eating fish caught there. The Corps of Engineers estimates that the remediation will take up to 15 years to complete and cost in excess of US$100 million. Cities and towns along its course include: Winona, Ohio Alliance, Ohio Sebring, Ohio Newton Falls, Ohio Leavittsburg, Ohio Warren, Ohio Niles, Ohio McDonald, Ohio Girard, Ohio Youngstown, Ohio Campbell, Ohio Struthers, Ohio Lowellville, Ohio Edinburg, Pennsylvania Mahoningtown, Pennsylvania Floods The Mahoning river is susceptible to frequent flooding during high rain events. A days long flood lasted almost continuously from March 23 to March 26, 1913. Youngstown residents were without water. Damage reached to communities throughout the area, such as Leavittsburg and Lowellville. Losses to the busy industrial area in the region reached the millions of dollars. Flood waters nearly reached the roofs of Republic Steel's plant. Some damaged bridges collapsed. Several water control infrastructure projects followed: The Lake Milton dam was built from 1913 to 1917. Another dramatic flooding event started when three days of