I had always assumed that the hay wagon in the famous painting was fording a shallow river that flows off between the trees in middle of the painting.
Mrs W and I visited National Trust, Flatford on Sunday, and took the obligatory 'gate crashing The Hay Wain' photo in front of the cottage, which still looks exactly the same.
Two things struck me:
1. That is not actually a river, it is a pond (or non-flowing side-arm of the actual river, or however you wish to describe it), which ends roughly where the trees in the middle of the painting are. Nobody would be daft enough to ford it, they'd just go round it, which would take about one minute. So the event he painted never happened.
2. While the cottage looks exactly as it did, the National Trust haven't bothered to instal a hay wagon in the middle of the pond, which would enhance the overall visitor experience and make those photos all the more enjoyable. Especially if you could wade out and pose on it, like the zebra crossing in Abbey Road.
Lest ye think this is some sort of sacrilege, there are precedents for this, i.e. statues commemorating something that never happened or somebody who never existed, which become visitor attractions in their own right, for example The Little Mermaid in Copenhagen harbour, Manneken Pis in Brussels or various Swords in the Stone dotted around anywhere with a vague connection to King Arthur. See also Waverley Station in Edinburgh.