The view from Lake Berkeley (updated Oct. 2017)

Nestled high up in the Rocky Mountains exists Montana's deepest lake.

The Berkeley Pit

The Berkeley Pit is a 1,780 deep open pit copper mine that is a half mile wide and a mile long.  In 1982, operations at the pit were halted and the giant pumps which kept groundwater out of the pit and old mine shafts under Butte were turned off.  Since that time, the groundwater level below the Butte Hill has been rising back to pre-pumping levels and filled the much of the 10,000+ miles of tunnels below town and also the pit, creating beautiful Lake Berkeley.

Lake Berkeley is not known for its fishing, it's best known as a potential time bomb.  The water in the pit has a PH of about 2.  The acidity of the water causes metals to dissolve and more sulfuric acid to form creating the positive feedback loop otherwise known as acid mine drainage (AMD) or acid rock drainage (ARD).  This does not bode well for most life forms.  I think everyone's heard the story about the snow geese by now (and then it got worse in November 2016).

Water treatment plant

A water treatment plant was built in 2003 to treat the water once it has reached a certain height but that won't go into operation for another 8-10 years. 

Another fun fact about the pit is that the walls sometimes collapse, making mini-tsunamis.  One of the largest landslides beached a research pontoon boat 40 feet above the water surface.

For now, the pit just sits there slowly filling.  MT Resources (the mine next door) used to mine the pit water for copper at a rate of 13 million gallons a day.  They are not currently mining the water anymore.

So, aside from the amazing history of Butte and the awe of human endeavor, why should people be aware of the pit?  Well, the pit and its sister lake, Yankee Doodle Tailings Pond lie at the headwaters of the Clark Fork River.  This is Montana's largest waterway and a major tributary to the Columbia River.  If anything catastrophic were to ever happen, there would be a lot of people and wildlife which would be very seriously affected. 

Another update is that the color of the water turned a beautiful green this spring.  Buttians attributed this to St. Patricks Day.  I've been told it's due to naturally changing chemistry as well as the fact that there is more copper at the surface because Montana Resources stopped mining it. Who knows?