I fish the river often with a 19 foot fiberglass bassboat, but you need at least on generator running to put your boat in and with one running you can fish from the dam down to Helm's landing which is about 6 miles downstream. You do still have to watch out for large boulders and stickups. With 2 or more generators running you can fish as far down as you care too.
If they don't have any generators running it's game over for fishing out of anything other than a small flat bottom aluminum john boat or smaller.
You can normally launch at the Kendall ramp right behind the dam, but that one is still shut down for repairs. There is also a primitive ramp down Ray Mann road which is about a mile below the dam. It'd be hard to do by yourself. You can also Launch at Helm's landing. It's a little better than the ramp at Ray Mann rd. and has better parking.
Hope that helps. And be careful. The river is very unforgiving and takes no prisoners. People underestimate how dangerous that waterway is.