Why our canals collect so much of the stuff

Anyone who has spent a season on the cut has felt that sickening lurch when the engine note changes and the boat slows for no good reason. Canals are wonderful places to cruise, but they are also slow-moving, shallow and lined with trees, which makes them excellent traps for every floating thing that finds its way in.

Debris gathers where the water slows or changes direction. That means the approaches to locks, tight bends, bridge holes, and the sheltered stretches beside moored boats and overhanging willows. Autumn brings leaves and twigs, spring brings cut weed and nesting material, and after heavy rain you will often meet a fresh tide of branches, bottles and plastic carried down from the feeders. None of it is personal — but all of it can ruin a pleasant afternoon if you are not paying attention.

Reading the water before you hit it

The best way to avoid a fouled propeller is to slow down and learn what trouble looks like from the tiller. Give yourself time to react and you will spend far less time hanging over a weed hatch.

• Watch for boils and swirls — a patch of water that rises or ripples differently from the flow around it usually means a submerged object or a silt bank just below the surface.
• Look for lines of bubbles or a slick sheen — both often mark a plastic bag or a sunken log that is just deep enough to miss your eye and just shallow enough to catch your blades.
• Note the colour changes — darker patches in an otherwise bright channel can mean a hole or a weed bed; lighter, sandy patches often mean a shallowing bar.
• Beware the tempting shortcut — cutting the inside of a bend or hugging the bank to let another boat past is where most props meet their match.

If you can, follow another boat at a sensible distance through a known bad stretch. They will stir things up and, if nothing else, you will see where they slow down.

The plastic bag problem

Bags are the classic canal enemy because they sit low, fill with water and sink just below the surface, where they are almost impossible to see until the propeller is already wrapped. They rarely damage the engine directly, but they can cut your speed, overheat the cooling system if they block the intake, and leave you manoeuvring awkwardly near a lock approach.

There is no magic trick, but a few habits help. Keep your speed modest in built-up areas and near shopping trolley territory — usually anywhere within a mile of a town centre. Avoid nosing into the very shallow margins where rubbish collects. And when you do spot a bag drifting ahead, make an early, gentle course change rather than a last-second swerve; a slow, deliberate detour is much safer than an emergency turn.

Clearing a fouled propeller safely

If the engine note changes, the boat vibrates, or the revs rise without any corresponding speed, assume you have picked something up. The first move is to knock the gearbox into neutral, let the boat glide, and switch off the engine. Do not be tempted to give it a hard burst of reverse first — that often wraps the offending item tighter.

• Secure the boat — tie up properly, or at least hold position with a pole or mooring pin, before you go anywhere near the hatch.
• Never open a weed hatch with the engine running, and always take the key out of the ignition so nobody can start it by accident.
• Use thick gloves — fishing line, wire and broken glass all hide in weed, and canal water is colder than you expect.
• Cut rather than pull — a sharp knife on a lanyard makes short work of rope and monofilament that will not unwind.
• Check the cooling intake while the hatch is open, and clear any leaf litter from the grille.
• Refit and reseal the hatch carefully — a poorly seated hatch is a much bigger problem than the weed you just removed.

If the obstruction will not shift, or you are in a deep, windy spot, call for assistance. There is no shame in it, and plenty of boats have been lost to a stubborn prop and a rising wind.

Handling shallow stretches

Half the battle on shallow water is knowing that you cannot bully your way through it. Drop your speed, keep the revs low, and let the boat find its own line. Keep to the centre of the channel where the original dredged profile usually survives, but be ready to move slightly off-centre if you feel the hull start to drag.

Moving crew and ballast weight forward can lift the stern and reduce the chance of the propeller stirring up the bottom. If you do run aground gently, resist the urge to blast astern — that sucks silt into the blades and can damage the bank. A pole, a patient reverse at low revs, or a helpful push from another boater will usually do the job.

Leaving the habitat better than you found it

Everything you pull off your propeller is part of someone's home. Weed, reed fragments and small creatures should go back into the water, not onto the towpath. Tip them in a few metres away from the boat so you do not simply scoop them up again, and try to avoid running through floating rafts of weed unless you have no choice — they shelter fish fry and invertebrates.

Be especially mindful between March and September, when nesting birds and young waterfowl are everywhere. Keep well clear of reedbeds and overhanging vegetation, and slow right down for swans and their cygnets. If you pick up fragments of invasive plants such as floating pennywort or Azolla, bag them rather than returning them to the water, and clean your prop and hull before moving to a new waterway.

Above all, talk to other boaters and to the lock keepers you meet. Local knowledge about which stretch collects rubbish after a storm, or which corner always hides a shopping trolley, is worth more than any handbook — and it is freely shared over a mug of tea at the next lock.