Eddies are your friend! All good boaters catch eddies and use them to control their descent downstream. A good rule of thumb in paddling is to never leave an eddy until the coast is clear from above and you can see how to reach an eddy below. Here is an excellent diagram of an eddy:

Eddy lines (or fences) can sometimes be tricky to navigate. The main body of water rushes downstream and the current in an eddy runs back upstream. Between these to opposing currents is the eddy line. When catching eddies, we puncture the wall perpendicularly and drive/pull across them. If your angle of attack is closer to parallel, you will bounce along the eddy line. Here is a nice video that explains and shows eddy lines: Eddy Lines