 The ditch on the other side of the road is the source of the River Little Ouse which continues the county boundary and, via the Great Ouse, reaches the sea at King's Lynn.It is thus claimed that during periods of heavy rainfall Norfolk can be considered to be an island.The explanation of this oddity is that the valley in which the rivers rise was formed not by these rivers, but by water spilling from the periglacial lake known as Lake Fenland.