Reverse your boat into a winding hole. The apex of a winding hole is normally the shallowest part of it, gets no traffic movement and therefore may silt-up almost to the surface.
Tie up with any part of your boat within 100 feet either side of a winding-hole. Full length working boats may need to turn at any time of the day or night.
Pull out from the bank when a boat is coming on in the same direction of travel which you intend to follow. Likewise if a boat is nearly finished locking-through in your direction. This is the height of bad manners (like pushing into a queue).
Exceed the speed limit of 4 miles per hour. This is about the speed of a fit person walking along the towpath so beware if you find yourself catching up with towpath walkers or find that you are pulling away from those walking behind you. Excessive speed causes erosion of banks not protected by piling.
Pull a breaking wash but instead slow down until this phenomenon is no longer present. Breaking wash is caused by excessive speed and erodes banks. In places where the canal has very shallow water such a breaking wash can be created at speeds below the 4 m.p.h. speed limit and greatly exacerbates bank erosion.
Lift the paddles on a lock which is not at least half full/empty in your favour without first checking whether there is traffic travelling in the opposite direction to you who which will benefit from the state of the lock with less waste of water. This may involve walking through a bridge 'ole if this is blocking your view along the next pound.
Close paddles which you find lifted, or close a gate which you find open, without first checking that the lock has not been 'set' for an oncoming boater (who is possibly working solo).
Lift a paddle to fill or empty a lock when a boater is engaged in manoeuvring to the side of the canal within several hundred yards of that side of the lock
Cut corners. The water movement on a canal or a river is always round the outside of bends and silting up takes place on the inside corner. Entry onto shallow water can (and frequently does) lead to loss of control, particularly of steerage, and resultant collisions with other craft or with the bank.
Tie on the outside of sharp bends. No matter that mooring rings or bollards may have been placed there by ignorant landlords or even by canal staff who may have never in their career seen a loaded working boat negotiate a sharp bend or that there is convenient piling to which you could attach piling hooks. A loaded working boat, and some of the longer and heavier leisure craft may need to steer very close to the edge to stay in the 'channel' and successfully negotiate the sharper bends.
Tie-up using a centre-line. The centre-line, which is usually affixed to a ring welded to the cabin roof at or near the center of yaw, is only for manually manoeuvring a boat and should never be tied off to anything on the bank or lockside. An ill-mannered passing boater travelling at excessive speed will, via a tied-off centre-line, cause a moored craft to heel sharply over with the risk of inside-cabin accidents particularly if cooking is taking place. Use fore and aft lines (and possibly a 'spring' as well) tied at least 5 feet forward and aft of the craft to tie-up for the night or moor for longer periods.
Slown right down (engine at idling speed only, just sufficient to maintain steerage way) when approaching a boat drawn into the side but which cannot be readily seen to be tied-up.