Walden Pond is the 17th-century geographic place-name given to a ~25-hectare lake that, because of Thoreau's Walden, became the literary fountainhead of America’s environmental consciousness and the world's most famous kettle lake. The early (1846-1854) dates for his detailed technical, spatial, hydrologic, thermal, and ecologic observations, measurements, hypotheses, inductions, and publications indicate that Lake Walden is also the birthplace of American limnology.

Recharged almost exclusively by groundwater from a sandy glaciodeltaic aquifer, Walden Pond is a flow-through lake described accurately in Thoreau's masterpiece as “a clear and deep green well.” Normally, Lake Walden is continuously coalesced above three separate kettles, the westernmost being the focus of the vast majority of Thoreau's observations. This is Lake Walden's largest and deepest basin, a ~17-hectare, symmetrical, star-shaped, cove-outdented, sinkhole responsible for the literary holism of Walden. This basin was created by the delayed meltdown of a discrete block of stagnant Laurentide ice buried by an ice-recessional delta graded to ice-dammed Glacial Lake Sudbury. That block detached in a locally over-deepened, rock-fracture-controlled, glacially eroded bedrock basin within the thalweg of a Neogene fluvial strike valley cut into exhumed Paleozoic rock.

Thoreau's close readings of the glaciological writings of Charles Darwin, Elisha Kent Kane, and James Forbes, combined with his own field work on outer Cape Cod, allowed him to accurately induce the glacial origin of Walden Pond and to predict a future return of the ice sheet. Though Thoreau's technical understanding of the glacial theory is revealed in his voluminous private Journal, he avoided being explicit when publishing Walden, swapping the science for myth, metaphor, allegory, and synecdoche. He did so to guard against the book's commercial failure and to tease the scientific consensus for officially endorsing the erroneous theory of catastrophic iceberg drift.

The Lake Walden of Walden (1854) broadly resembles that of the earlier Holocene Epoch and the later Anthropocene Epoch. But in detail, it is greatly changed everywhere, especially its shore, trophic status, and climatic phenology. Thoreau's specific technical observations provide a historic baseline (1822-1861) for modern scientific studies. His well-reasoned prediction of future glaciation has since been thwarted by anthropogenic greenhouse warming. Ironically, he wrote the bulk of Walden in a house heated by coal.