The open-pit mine was in operation until 1982 when the dewatering pumps were turned off and the pit filled with water. Well, you can almost not call it water since it is so saturated with copper that miners are able to mine copper directly from the water. The acidic water does not only contain high concentrations of copper but also sulfuric acid, iron, cadmium, arsenic and zinc. With a pH between 2.5-3.0 it is as acidic as vinegar. If you would drink a bottle of the water it would form a corrosion layer in your digestive system meaning basically that you die of rust.
The pit is 540m deep and filled with acidic water to a depth of 270 meters. It is thus remarkable that bacteria, fungi and algae manage to survive in the lake. More than 100 types of microbes were discovered in the lake by Don and Andrea Stierle. It is natural selection at its height, since some of these organisms are solely found in the lake.
A flock of 345 snow geese landed in the lake in 1995 and died. The custodian of the pit first denied this was due to the toxicity of the lake and claimed it was due to a ‘grain infection’. However, the state of Montana revealed that the insides of the geese were filled with burns and sores caused by high concentrations of arsenic, copper and cadmium. Nowadays gunshots and loud speakers are supposed to keep the birds away from the lake.
In 2003 a water treatment plant was built near the northeast rim of the pit to prevent water levels from rising and contaminating the groundwater. Drinkwater is being pumped from high land reservoirs, since historic mining has already contaminated the valley aquifer. For now the Berkeley pit remains the only toxic lake in the world you have to pay (2 dollars) to visit.
Image: Courtesy of Barbara Oosterwijk. The Berkeley pit as seen from the viewing platform. If you look close you can see the reddish color of the water.
Dobb, E. 2000. New life in a death trap. Discover