| Acker Island | |
| Image Alt: | Aerial image of an island. |
| Pushpin Map: | United States Sacramento Delta#USA California#USA |
| Coordinates: | 37.9975°N -121.4489°W |
| Location: | Northern California |
| Waterbody: | Sacramento–San Joaquin River Delta |
| Area Sqft: | or |
| Area Acre: | --> |
| Length Ft: | --> |
| Width Ft: | --> |
| Coastline Ft: | --> |
| Elevation Ft: | 3 |
| Country: | United States |
| Country Admin Divisions Title: | State |
| Country Admin Divisions Title 1: | County |
| Country Admin Divisions 1: | San Joaquin |
Acker Island (also known as Lost Isle) is a small island in the Sacramento–San Joaquin River Delta. It is part of San Joaquin County, California. Its coordinates are 37.9975°N -121.4489°W, and the United States Geological Survey measured its elevation as in 1981. It appears on a 1952 USGS map of the area.