HC, looks like you have some good rivers out there. My advice is to start small and avoid rapids until you get the hang of whats going on.
Remember to scout the runs you want to swim for hazards ahead of time. When swimming constantly look ahead, both above and below the water for obstacles,( like barb wire, a tree or an old car)
Take the time to learn your rivers and seek out the local rafting& kayaking community. They won't understand the snorkeling thing, but they do know when a river has a new hazard in the water, or there is a low head dam to avoid.
I would recommend learning in an area that has easy access to a small riffle and a good set of pools. Start small and learn to understand the dynamics of moving water in an area with a safe tail out. You can park and play in one spot, alternately swimming and crawling against the current and drifting back down. Rapids create lots of bubbles, making visibility go to zero, a real great way to get a boulder to the face.
Try and talk one of your friends who is a solid swimmer into your crazy adventures, it's more fun and
potentially safer. Not too many divers here swim solo because it's dangerous. In short, awesome stuff, but be careful.
A basic google search for your areas turned up this river resource. Looks like there are conservation and paddling groups active in your area, chances are they would be glad to have a new member and you can glean your new friends experiences for beta.
Paddling Clubs
Here's the link to my videos to get you stoked but remember, there is no PADI, no active community of river snorkelers, nobody telling you that it's stupid, unsafe or totally awesome. It's up to you to keep yourself safe.
Here's my vimeo page to get you stoked, there's a link there to the Facebook community for river snorkeling.
https://vimeo.com/riversnorkel