the Ohio's pretty strong, especially with the Tennessee and Cumberland rivers flowing high at the west end. Lots of rain came up through western Tennessee, Kentucky, and up into Ohio before it worked its way out of the Mississippi watershed. That'll work its way down to NOLA soon enough. Hopkinsville, KY was flooded this morning, after having endured rain for the last couple of days from a stalled cold front that was being drawn together with Katrina.
I can't say that it's a huge total amount of water, but the Mississippi will flow a bit above average for a couple of days, IMHO.
Actually the Ohio has more flow than the Mississippi does at Cairo, IL, which is south of the Missouri/Mississippi Confluence. Just an FYI.
The Ohio is pretty low, It will taker a lot of water to fill it up.