A big river

We've had no chance to get milk or bread or anything, so we stop at the A38 bridge and I walk up to a garage. It's deserted and it takes some time for the man to appear behind the counter. I have stocked up a bit and he seems bemused.

"Why don't you shop at a big supermarket or somewhere? It'd be a lot cheaper."
"We're on a boat and this is the first place we've come across that has a shop."
"A boat?"
"Yes. A boat." I think he'd have been less surprised if I'd claimed to have beamed down from a spaceship. "There's a canal just down the road. About 100 yards away."
"You're the first people who have ever come here from the river. Is it a big river?"

Ho hum.