Silver is found in the elemental state and in combined ores such as argentite, hornsilver, proustite, and pyrargyrite.
From these ores, silver ions may be leached into ground waters and surface waters, but since many silver salts such as the chloride, sulfide, phosphate and arsenate are insoluble, silver ions cannot be expected to occur in significant concentration in natural waters.
Metalic silver is stable over most of the range of pH for natural water except when dissolved silver is present at a high pH. Then it becomes very toxic, especially to aquatic organisms. The stickle back, an extremely tolerant fish, has been known to succumb at levels as low as 0.003 mg/L.