PILLOW Water that is piled up by the current against an obstruction that is not entirely submerged. Water is compressed but flows around it.
FERRYING causing boat to move laterally across the current, usually to maneuver around obstacles, work eddylines, etc. "Back" ferrying puts the bow pointing downstream; "Front" ferrying faces the bow upstream. In fast current, the ferrying angle should be narrow; in slow current broader.
UNDERCUTS/POTHOLES submerged hazards that dont usually affect passage overhead but can trap a capsized paddler under the edge of a riverbank or rock ledge, or entrap a victim against a rock or in debris settled into a pothole.
ENTRAPMENTS Anything that can snag/hold one underwater, from the force of water preventing them from swimming free or clothing/items becoming snagged on the obstruction (branches, rock points, etc.).
SWEEPER branches hanging low over or into water that can sweep a paddler from the boat.
STRAINER Often used to describe a sweeper under water. Branches act like a sieve that keeps victim/boat/gear from passing through. Oftentimes loose objects get snagged by strainer branches, thereby holding victim below the surface.
DAMS Probably the most formidable of all man-made structures. These must be portaged. To go over a dam is to permanently terminate your existence! Dams and dam-like structures (weirs, spillways, ledges) come in a variety of sizes but all form an obstruction completely across a river. Severe hydraulic action occurs at the downstream base of these structures.
WING DAMS These are small, dam-like structures protruding out from the bank of a river to define the channel. They are angled downstream at varied intervals.
CLOSING DAMS Not so much a hazard as a nuisance. These go from shoreline to shoreline completely blocking a side channel.
BRIDGES, ETC. The bases of these structures can create eddies, collect debris that can act like strainers and cause the current to react in myriad ways.
STUMP FIELDS As part of the creation of pools behind dams, trees were cut prior to the flooding of lowlands. Many acres of stumps lie submerged just below the surface throughout many of these pools.
TRAFFIC WAKE Barges are restricted to the main channel in rivers with dredged channels. Their wake and churned up water can be dangerous to small craft. Stay clear of commercial river traffic.
OTHER HAZARDS common to all bodies of water are the natural elements of wind, lightning, fog and even the water itself (hypothermia, for example).