There have been three watershed/biological studies on the Mahoning river that have been done in 1995, 2002, and 2012 showing the historical changes in the in the Mahoning. The river has changed for the better and the future will hopefully be even brighter.
1995 study: https://epa.ohio.gov/portals/35/documents/mahon94.pdf
2012 study: https://epa.ohio.gov/Portals/35/documents/USSteelMcDonaldTSDfinal.pdf