The dying of trees on the northern bank of the Orange River is restricted to the area of the Daberas diamond mine. Water samples were taken from upstream and downstream of the mine to determine the influence of the mine on the ground water quality. The mining operations cause an increase in salinity of the groundwater from 8000 to 15800 mg/L, mainly due to an increase in NaCl but also due to increasing amounts of K, Ca, B, Br and Sr. Other major constituents of the groundwater, like Mg and SO4 , are only increasing slightly. The fingerprint of the mining operation in the groundwater is characterized by an increase of nitrate (by 346%), nitrite and ammonia as well as chromium (by 160%). The increase in salinity traces back to dissolution of continental evaporates in the river sediments by seepage from the tailings dump, and to an increased evaporation in the mining area, especially at the surface of the tailings dump. To prevent the further dying of trees and to trigger re-vegetation, the flow of highly saline groundwater from the mining area to the river banks has to be prevented. It is recommended to collect the saline groundwater in trenches downstream of the tailings dump. A potential source of groundwater contamination is ferrosilicon (for dense media processing), which is released in significant amounts with the tailings material. It contains higher concentrations of heavy metals than ferrosilicon used by other diamond mining companies in Namibia.