And that that causeway had no gaps until 2016.
No, the full causeway as originally constructed in the 1960s had a pair of culverts to allow some water exchange. Then in the wet years of the early 1980s, the south half of the lake rose so high that it threatened to flood some of the outlying areas of SLC, and the existing culverts weren't doing enough to equalize the lake levels, so the causeway was breached near the west end in 1984 (that's what
this is). The issue was that in the early 2010s both of those culverts had to be closed I think because of issues with subsidence, and then a multi-year drought dropped the lake below the level of the 1984 breach. So for a few years, there wasn't any water exchange until the causeway was breached again in 2016.
And that Great Salt Lake is shriveling up so much that Antelope Island is no longer an island anymore.
Antelope Island hasn't been an island since 2001 and actually requires a higher-than-average lake level (average is 4200 feet elevation) to be isolated from the mainland. The more noteworthy stat there is that there are currently no permanent islands beyond temporary sandbars or minor stuff like that. The last ones to go are Gunnison Island (4193 ft) and Fremont Island (4195 ft), and have been islands as recently as a couple years ago... but the lake currently stands at about 4191 feet.