During the summer, if a waterbody is deep enough to stratify into three distinct layers, with one warm layer on top, one cold layer at the bottom and a layer of rapidly changing temperature in between (called a “thermocline”), then it is a “lake,” while a waterbody with one or two weakly defined layers is a “pond.”

Scientifically, there is no universally agreed-upon size that distinguishes a lake from a pond, but the most common distinction is based on depth and sunlight penetration. In the field of limnology, a body of water is generally considered a pond if it is shallow enough that sunlight can reach the bottom across its entire area, potentially supporting rooted plant growth from shore to shore. A lake, conversely, has a "pelagic" zone—a deep area where sunlight cannot reach the bottom, creating a dark, cold layer of water that does not support rooted plants. Some experts also use "thermal stratification" as a metric: lakes are deep enough to form distinct temperature layers (thermoclines) in the summer, while ponds are usually a uniform temperature throughout. While terms like "pond" and "lake" are often used arbitrarily in naming—like a large "Island Pond" or a tiny "Echo Lake"—the grounded 2026 ecological consensus focuses on whether the sun can "see" the bottom of the entire basin.