Some ponies say it's no skill to pull a canal barge, but Mersey knows better. Even algae on the bottom makes the barge pull differently than when it's clean, and its momentum can be a help or a hinderance, depending on the situation.
Locks, docks, and opposing traffic all need to be dealt with, as well as an extra barge in Fens Junction that's going all the way through to Stroudwater. If that wasn't enough, she's got to look after her brother and keep him out of trouble, both on the canal path and at the public house.