It depends on who you ask: there's no universal definition of what constitutes a lake or a pond.
The Ramsar Convention, which covers wetland protection in over 150 countries, considers anything under 8 hectares (just under 20 acres) to be a pond.
Most states have a legal definition of what constitutes a lake based on area, generally around 10 acres. Some states consider all natural bodies of non-flowing water to be lakes. Minnesota, the "Land of 10,000 Lakes," uses this definition. There are actually 11,842 legally-defined lakes in the state, and while some of these may be quite small, nearly all of them were created naturally by glaciers.
In Canada, a lake is defined as any non-flowing body of water with a defined coastline that is large enough for someone to swim in, provided it's warm enough.
There are a few more general definitions:
...have surface waves preventing plants from growing on the shoreline.
...are deep enough that sunlight doesn't penetrate the bottom enough to support photosynthesis.
...are deep enough that there are temperature variations between different depths.
...are large enough that they cannot freeze entirely.
...have enough thermal mass to influence local weather patterns, i.e. "lake effect" snow.
...can occur naturally, or by building a dam on a river.
...are shallow enough that rooted plants can grow at the deepest points.
...can freeze completely in cold enough weather.
...are man-made, but have not been created by a dam.
Lakes and ponds have different internal currents, caused by varying temperature differences in the water. However, no one has come up with a definitive rule for this phenomenon.
There's also the expression "across the pond," which refers to anything on the other side of the Atlantic, say, a Briton talking about something in the United States.
Posted 4272 day ago