From San Francisco:

HWY 80 (Bay Bridge) to HWY 880 South
Exit Marina Boulevard (west bound)
Marina Boulevard ends at San Leandro Marina

From Pleasanton:

HWY 580 West to HWY 238 South
HWY 238 to HWY 880 North
Exit Marina Boulevard (West bound)
Marina Boulevard ends at San Leandro Marina

From San Jose:

HWY 880 North
Exit Marina Boulevard (West bound)
Marina Boulevard ends at San Leandro Marina