Working in fast moving water

[Vtach]

After thinking about it for a bit, I had talked with someone about this a few years ago and I remember them talking about using some form of anchoring system which utilized 2 grapples, one to set and one to move.  I don't recall if they were a sand anchor, fluke or hook style.  That combined with a bunch of lead, enabled them to work on and along the bottom. 

One thing to consider if trying to use a form of zipline is that the line will always be above you and due to the vector angle the current is probably going to end up pushing you toward the surface if you will be "head up" for filming.

Whatever system you use, make sure to have a quick release and get a good read on the river before diving...strainers suck.  Good luck