- Category: Water Feature
- Type: Island
- Latitude/Longitude: 49°55'23"N 6°18'8"W
- Eastings/Northings: 91304, 11442
- OS Grid: SV913114
- Mapcode Local: GBR BXTW.HZC
- Mapcode Global: VGYC4.Q604
Location and coordinates are for the approximate centre of St Mary's within this administrative area.
Geographic features and populated places may cross administrative borders.