Current densities of 2.5*10-4 amp/m2 can be generated by constant groundwater migration in artesian aquifers. These DC currents are sufficient to generate magnetic anomalies exceeding 200 nT in both the Menindee Trough (Australia) and the Karoo Basin (South Afrca). Telluric currents associated with ionospheric activity can be detected by variations in magnetic induction but constant offsets associated with streaming potentials and geochemical activity (SP anomalies) are obscured by noise. Consequently some regional magnetic anomalies may be wrongly attributed to variations in magnetic susceptibility with residuals explained by remanence.