Below are some of John Blyth's pictures of the main ledges of the Slave River.
For current water levels, check out the Alberta water level gauges website and select the gauge at Fort Fitzgerald.
For good stories about the Slave, check out Leif and Natalie's blog posts. It's has tones of details on how to get there and the kinds of conditions you can run into.
Remember that the river is 2km wide in some areas, and it can be very challenging to pick the right routes when not familiar with the river. It is wise to talk to the locals before attempting to get out there on your own.