The lower pool is a more likely candidate for the wonder. It sits in a small triangular hollow off the side of the main floodplain, presumably where a tributary stream cut through the glacial sediments to the limestone bedrock (Photo). While the resurgence doesn't appear to be in the place it once was, just a few meters round the corner the main floodplain is nearly permanently under water, with a thick covering of marsh plants. A clear area next to the Whirly Pool site may indicate resurgent flow (Photo). The Parish boundary ran down the channel that drained the Whirly Pool (1775 Map), parallel to the fence in the photo, which follows an 1800s(?) drainage channel down to the Troggy. That the boundary kinks here may indicate the flooding was there when the boundary was defined, possibly in the Dark Ages (See Science). Certainly the land has flooded for some time1. You can actually walk down under the M48 pilings shown on the photo along a footpath (Map), which is a good spot to view the flooded "lake" and the location of the lower Whirly Hole (Photo looking towards the site; Photo looking away from the site). By way of interest, the motorway pilings appear to have obliterated an additional spring which is marked on older maps as a "Holy Well" 1887 Example.
Conveniently, the location does match the wonder description quite nicely, as there is a large bank a couple of hundred meters downstream which, if the tide reached the pool, you'd expect to get wet (Photo). Of course, once you go looking for such things, it is easy to find them, but the feature is at least distinct enough to be known locally as "The Bank".