You've probably seen it as it's had a lot of publicity. It used a variety of proxies to show, apparently, that the climate had been pretty steady for millennia (the 'handle' of the stick) and from around the year 2000 onwards there would be a rapid ascent of temperature (and by implication other climatological indicators) largely as a result of anthropogenic carbon dioxide emissions (in other words, the upturned 'blade' of the stick). This is not without criticism, in particular concerns about the highly selective use of indices and the 'flattening' of well documented fluctuations in the past such as the little ice age, the mediaeval warm period, the Roman warm period, the Minoan warm period, and further back, the holocene transgression and so on. Interestingly, Mann himself has backed off somewhat from the hockey stick graph, and even says it wasn't really his idea.
Anyway, back to the hydrology of Marsh Lane. Here's an aerial photo off Google Earth Pro from 2014:
View attachment 305359 Look at that pattern of discolouration on the crops that comes up from the south and includes a bit of the field to the west of the cottage and then appears to curve back eastwards, taking in the pond in the trees, which is probably part of a former oxbow lake. Looks like a former river channel to me. The current channel of the River Avon is just to the east. So before it was all ditched and banked and cultivated the river might well have been much closer to the house.