A gongoozler is "a person who idly watches the labours of others while declining to offer assistance or becoming involved. Traditionally a term used by canal bargees when referring to onlookers found clustering around locks and moorings where barges have to stop and the crew engage in sometimes hard physical activity to make progress." (urban dictionary)
There are always gongoozlers at the Foxton Locks (two staircases of five locks each). Indeed, my wife and I started out as gongoozlers before taking up the canal trips actively.