"The way you read it"...read what?
The direct disharge of waste from the toilet and/or dumping a tank is illegal in ALL US waters. The discharge of TREATED waste from CG certfied Type I or II MSD is legal in most waters of all navigable interstate inland rivers, including the TN-Tom system...although there are few areas--those that are municipal water supply impoundments--that are "no discharge." Not all of 'em are included in the EPA list. AL does have a marine sanitation law that pretty much follows federal guidelines...I'm not sure MS does. But whether they do or not, the USCG has jurisdiction in both their coastal waters and in all interstate waterways and federal law trumps state law in those waters. However, the discharge of treated waste is legal in AL and MS coastal waters and I know of no "no discharge" impoundments on any river in either state, only their non-navigable intrastate lakes--which don't all show up on the EPA list either.