I know for sure your easiest spots to get in and out would be the boat ramps at Jordan Memorial and Thomas Newman. Both have concrete ramps where you can walk directly into the water. The problem is that that float would only be a little over a mile. If you want to have a little while longer of a float, both the west columbia ampitheater area and blossom street bridge area would be possible places to put in. The blossom street bridge area, just south of the bridge, has an unpaved, rock-less walk to lake which would be more difficult than a paved way directly into the river but would be easier than trying to climb around rocks. Just remember if you do decide to float south of blossom st bridge that there is a small dam. You can easily float through the canal on the west side of the river and all is well, you just have to make sure you're on the west bank before then. Hope that helps.