It is an island now, but this wasn’t always the case! As mentioned in Wikipedia, Alameda was originally a peninsula off Oakland — but the need for expanded shipping facilities in the late 19th century led to a shipping and tidal channel that was dug between Alameda and Oakland cities in 1902, extending and deepening the natural estuary, which resulted in Alameda becoming an “island”.
These maps confirm Alameda’s island status 🙂
Alameda Musings 