This work is intended to study the groundwater potential of Lagos Island in Nigeria and delineate
appropriately, the depth at which saline water intrude into the groundwater resources of the area. Saline
intrusion into groundwater resources of Lagos Island has rendered potable percentage of undergroundwater
undrinkable. Better understanding and proper delineation of the saline water will proffer
efficient household use of the resource. A direct current electrical resistivity method of geophysical
prospecting using the Schlumberger electrode configuration was adopted. Electrical resistivity with
natural gamma was carried out to accurately delineate prolific sand aquifer(s), determine the exact lithology
of the well and nature of saturated fluid at Lagos Island. The same test was repeated at Lagos
Inland in order to proffer engineering control techniques that will be necessary for controlling saline
intrusion into inland groundwater. Quantitative interpretation of curve types obtained from the field
data of the sounding curves revealed that the site is underlain by topsoil, clay, sandy clay and saline water
sand intercepted at a depth of 136 m. Groundwater development through deep borehole drilling is
recommended to a minimum depth of 220 m; the borehole depth should not exceed 250 m. Technique
for controlling seawater intrusion into inland groundwater should include construction of subsurface
barrier in excess of 136 m deep perpendicular to the coastal creeks and lagoons