A functional definition to distinguish ponds from lakes and wetlands
nature.com
nature.com
I spent a few years building ponds and lakes and levees and dikes and such in association with people who had spent entire careers doing so. That was the "common wisdom" opinion.
There's been considerable legal fuss over the question of "how wet does land have to be, for how long, to be 'waters of the United States' for the purposes of regulation."
In fact, I know an artificial pond (and I guess there are many) that has no obvious inflow, but if you look closely and feel the waters 1-2 m below the surface, you realize it has massive inflow from ground-water (there is a large river just nearby), and there is a swampy area at the opposite end, where the pond has considerable outflow - just not as obvious.
Now we could modify this to say, there must be obvious inflow from a river, stream or similar... But then again, in areas where there are not many big lakes nearby, e.g. Lower Austria, there are several "lakes" (often artificial) which I always jokingly criticize ("You call that a lake?").
If you grew up near e.g. Lake Constance or let's say Lake Michigan, most "lakes" are ponds for you, even if they have inflow.
So I think most people would agree that surface area is the main differentiator, but I would say it is highly subjective where you draw the line.
Major groundwater engineering projects were also used in early Mesopotamia to inhabit otherwise unlivably dry areas. You'd dig a series of wells between the site and a mountain, with a tunnel connecting the bottoms of the wells. Water collected in the wells and flowed down the tunnel to the village.
Definitely, to me it's not really a lake if you can see the entire opposite shore.
The paper is more concerned with whether the body of water provides a ecological service rather than a hydrodynamic.
Of course, to confuse matters, a lake becomes a pond if damming was done by beavers.
Note that by the proposed definition, all rivers and all segments of any river are lakes; outflow is always equal to inflow for any persistent body of water.
Personally, I'd be more comfortable choosing whether to call Lake Travis a "river" or a "lake" based on whether there's a current on the surface. If yes, it's a river. If not, why not call it a lake.