IMO whoever dumped the body next to the river did not have access to a boat. If they had a boat why not conceal the body inside the boat on land then take the boat to the river and go out and dispose of the evidence. It just doesn't make sense to transport the body to the rivers edge, then go get the boat and go back to pick up the body then take it out to dispose of it in the water.
I know, that was my big hangup with the boat theory. It would be far easier and less suspicious to load the body directly into the boat before leaving Wenatchee.
But then I remembered the river level was so extremely and unusually low at that time. I've rarely, if ever, seen the river that low.
The river being so low would make it impossible for a person to launch a boat at the CB boat launch. Also, it is likely the river was too low to even drive a boat out of the channel.
There is a second less well-known boat launch on CB island, but a lot of people don't know about it. It took me 8 years to learn of its existence.
There are only 5 boat launches between Rock Island Dam and Wanapum Dam (going from Rock Island Dam down river to Wanapum Dam): (1) Spanish Castle; (2) Little CB; (3) CB; (4) CB Island; and (5) Sunland Estates.
Spanish Castle boat launch suffers from the same problems as the CB boat launch during low river levels.
Little CB is a bunch of private homes that are lived in year around, and the folks living there consider that boat launch to be their own private boat launch (though it is definitely public). So, the perps would be much more likely to be noticed at this boat launch. Plus, it's unlikely the perps knew about this boat launch.
Sunland Estates is about a 45-minute drive from CB. I don't think the perps would trailor a boat that far.
Therefore, the perps may have wanted to dispose of MC's body in the river via boat, but they were forced to move MC's body immediately and launching a boat on the river at that time was simply impossible.
FYI: The only public boat launch on the west side of the river between Rock Island Dam and Wanapum Dam is at Vantage.