This map seems, for the most part, to be fairly accurate. At first glance at least. But there are two very notable exceptions. The first, up north, is the lake straddling the border of West New Jersey and Pennsylvania.
The second is the giant "Apalache" lake down south. A couple of links from the page the map is on showed me that the lake was reported by John Lederer, but I'm not sure why. Were blank spaces on maps just filled in with wishful thinking? The "Arenosa Desert" doesn't seem to be much of a selling point for the New World.
I haven't really been able to find anything on the lake up North and it makes less sense to me. This map is from 1714 and the lake doesn't appear to be too far north of Philadelphia.
It is notable that the detail and accuracy of the coastline is pretty good, as though the cartographer was primarily concerned with navigation to and around the region. The mouths of various rivers are also noted, but they get more "impressionistic" inland- the Potomac heads far north into Maryland and Pennsylvania, the Rappahanock extends far beyond its origin in present-day Chester Gap VA, for example, beyond where navigation would be possible. The very-hopeful picture of a merchant displaying goods for trade to Indians suggests the map is marketed to a cargo-carrying vessel, not an inland traveler. And it does predate some knowledge of the inland geography: the "Knights of the Golden Horseshoe" expedition of Virginia Governor Spottswood would not cross the Blue Ridge into the Shenandoah Valley until three years later.
The Delaware does have a history of flooding, especially above Philly/Trenton, and what is today the Delaware Water Gap Recreation Area.
The land for that park was actually mostly first acquired as part of a plan to build a large hydro electric dam at Tock's Island on the river and create a lake upstream. In fact the flood levels in Bucks County PA, in the area where the lake is depicted, reached nearly 40 feet! And there are numerous now gone small lakes and the area could be a bit swampy with the rivers border poorly defined above Philly.
The dam and lake plan got pushback and eventually fell through and became a wonderful park, but it is certainly possible that the impression of a large lake if the maker was given bad info or misunderstood it could have gotten in.
