The 150 foot towboat Thruston B. Morton was pushing 8 barges loaded with dry cargo down the Ohio River when it veered off course causing 2 barges to break free.    The barges floated downriver until they allided with the Shawneetown Bridge which connects Old Shawneetown, Illinois with Kentucky.  The bridge was closed until transportation officals could do an inspection.   Officals reopen the bridge later after finding no signs of structural damage.   Coast Guard stated that high water and strong current caused the vessel to veer off course.