As coordinator of the Lakes of Missouri Volunteer Program I am frequently asked the question “what’s the difference between a pond and a lake?” I usually have a glib answer, like “if a cow can stand in the middle, it’s a pond,” or “if you tip your boat and your head gets stuck in the mud, it’s a pond.” In truth there is no universally accepted distinction. The difference between a pond and a lake is only semantic, and the characteristics that distinguish the two will vary by region.
Ultimately a small body of still water is a ‘pond’ and a comparatively larger one is a ‘lake.’ However, the precise surface area at which a pond becomes a lake is unclear. The pond/lake size division leans toward larger acreage in regions with abundant natural lakes. A water body of 200 acres might be considered a pond in the northeastern United States where natural lakes are abundant, while in Missouri a 200 acre water body would absolutely be called a lake. For folks who spend their weekends boating on lakes where they can’t see the far shore, 200 acres must seem like a pond!
Surface area is not the only variable used to distinguish ponds from lakes. Depth is often considered, with ponds often defined as being so shallow that the water mixes from top to bottom all year round. Conversely, lakes are deeper and will thermally stratify during the summer. Some define a pond as shallow enough that light reaches the bottom, allowing rooted plant growth throughout. Lakes on the other hand have areas deep enough that light won’t reach the bottom, thus excluding rooted plant growth. Finally, Some may use origin to distinguish between a pond and a lake, labeling a pond as a man-made body of water and a lake as a naturally occurring feature.
The criteria for categorizing still waters are numerous and often contradictory. Let’s take Rothwell Lake in Moberly as an example. It has a surface area of about 25 acres, and could easily be called a pond in other regions of the country, simply because of its (relatively) small surface area. However, according to our data, this lake stratifies in the summer, thereby making it a lake by one definition. Light will not reach the bottom at the center of Rothwell Lake and rooted plants will not grow there; thus, it is a lake by another definition. Rothwell Lake is a man-made impoundment, and thus a pond by yet another definition.
Ecologically speaking, it doesn’t really matter if a water body is called a pond or a lake. A water body deep enough to stratify is very different from a water body so shallow that it mixes throughout the year, regardless of its name. While surface area is probably the most common variable for distinguishing between ponds and lakes, it is not as ecologically important as depth. What likely makes area the most commonly used characteristic is the ease with which it can be estimated. A lake’s surface area can be estimated by looking at a map, while estimating depth requires multiple measurements from a boat.
The LMVP has been working with the Missouri Department of Natural Resources to develop nutrient criteria for Missouri’s “lakes.” As we moved forward, we needed to make a distinction between lakes and wetlands. We decided on the EPA’s recommendation of 4 hectares (10 acres) as the minimum surface area for a water body to still be considered a lake. The water must also be at least 3 meters deep (9.5 feet) to ensure stratification. Smaller and shallower water bodies would fall into the “wetland” category due to the overwhelming influence of bottom and shoreline sediments on overall water quality. So Missouri’s regional, semantic definition of a lake is a body of still water with a surface area greater than 10 acres and deeper than 9.5 feet. We did not define ponds.
The definitive answer is that there is no definitive answer. The lake or pond designation is a naming convention that varies by region. However, the absolutely clearest distinction I’ve read states that “if it’s 3 acres and it’s yours, it’s a pond. If it’s 3 acres and it’s mine, it’s a lake.”