Man-made path across a river that is passable at a low water level. Some have pipes underneath to allow water to go through, creating artificial siphons. At higher levels, most low-level bridges act like werids. Be careful.
Normally formed on the downstream side of a rock or similar obstruction under the water. The water piles up on itself, forcing aerated water back upstream and into the trough, creating a stopper wave downstream of the hole
When a boat is held against a rock or other obstruction by the current. Can be vertical or horizontal, and also under water, which is life threatening. Playboats are particularly susceptible to vertical pins in shallow drops, and the older longer boats to side pins