- Category: Water Feature
- Type: Island
- Latitude/Longitude: 50°31'34"N 5°1'41"W
- Eastings/Northings: 185473, 73994
- OS Grid: SW854739
- Mapcode Local: GBR ZG.PVVN
- Mapcode Global: FRA 07CN.T4F
Location and coordinates are for the approximate centre of Trethias Island within this administrative area.
Geographic features and populated places may cross administrative borders.