An analysis of TRI data [1] shows industrial facilities dumped 232 million pounds of toxic chemicals into more than 1,900 American waterways in all 50 states during 2007. The report [2] ranks the Ohio River first for toxic discharges, followed by the New River and the Mississippi River.
Links:
[1] http://www.ombwatch.org/node/10514#at
[2] http://www.environmentamerica.org/uploads/e6/53/e6534339a34197ea1c06a80f2b2db277/Wasting-Our-Waterways-vAM.pdf