Thoreau writes in his journal:
A dark, but warm, misty day, completely overcast. This great rise of the pond after an interval of many years, and the water standing at this great height for a year or more, kills the shrubs and trees about its edge,—pitch pines, birches, alders, aspens, etc .,—and, falling again, leaves an unobstructed shore. The rise and fall of the pond serves this use at least . . .
I have said that Walden has no visible inlet nor outlet, but it is on the one hand distantly and indirectly related to Flint’s Pond, which is more elevated, by a chain of small ponds coming from that quarter, and on the other hand directly and manifestly related to Concord River, which is lower, by a similar chain of ponds, through which in some other geological period it may have flowed thither . . .