Montana’s Worst Environmental Disaster Has Water So Corrosive, It Can Dissolve Boats

The Berkeley Pit, Montana

The Berkeley Pit looks like a regular lake until you learn what’s actually in it. Montana’s most toxic tourist attraction is a mile-wide copper mine that’s been filling with poisonous water since 1982.

It’s deadly to birds, straight-up kills fish, and has enough acid to dissolve a boat. But hundreds of people still visit every year to see this technicolor disaster for themselves.

The Pit’s Mining History

The Berkeley Pit produced enough copper to pave a four-lane highway four inches thick from Butte to Salt Lake City and 30 miles beyond.

The mine was opened in 1955 and operated by the Anaconda Copper Mining Company until its closure in April 1982. This massive operation created North America’s largest truck-operated open-pit copper mine. Today, the pit affects about 2,800 acres of land and holds more than 50 billion gallons of contaminated water.

The Water is Insanely Acidic

When old mining tunnels exposed certain minerals to air and water, they created sulfuric acid. Thereafter, the water in Berkeley Pit became extremely acidic, with pH levels ranging from 4.1 – 4.5, similar to vinegar or cola. It’s already recognized as one of the largest Superfund sites in the U.S. by the Environmental Protection Agency (EPA).

It Pollutes Everything Around It

According to research by the CK-12 Foundation, the pit’s acidic water contaminates groundwater aquifers with heavy metals like copper, iron, arsenic, cadmium, and zinc, which leach from the rock.

Due to acid rock drainage, groundwater interacts with exposed sulfide minerals (like pyrite) creating sulfuric acid and dissolving the metals further. This results in metal-rich water that’s unfit for drinking.

This Toxic Lake is DEEP

The pit drops down 1,780 feet with about 900 to 1,000 feet of that depth. Deep in the pit, a mineral called iron pyrite (also known as fool’s gold) mixes with water and air to make more acid.

This starts a chain reaction where more metals dissolve from the rocks. It’s like a giant chemistry experiment that never stops. The Berkeley Pit currently holds about 50 billion gallons of toxic water.

Life Has Found a Way to Thrive in the Deadly Pit

Tiny organisms like fungi and bacteria have found ways to live in conditions that would kill most other living things. These tough microbes don’t just survive, some consume the metals in the water while others make special proteins.

The low pH creates an environment suitable for microbes like Hansenula anomala and Chlamydomonas which can grow at a pH as low as 2.5, demonstrating an adaptation to extreme acidity.

The Lake Has Killed Hundreds of Birds

Birds often mistake the pit’s shiny surface for a safe place to rest, especially during storms. Unfortunately, the toxic water quickly damages birds’ insides even if they only drink a small amount.

A tragic event in 1995 showed exactly what the pit could do: 342 snow geese turned up dead near the lake’s waters within days. Right after, a bird hazing program was implemented using loud noises and rifles to deter birds from landing in the pit.

The Water Changes Colors

All the dissolved metals make the water’s surface look like a giant mirror. What you see might range from deep orange to bright blue-green, depending on the chemical reactions happening below.

On clear days, the water is so reflective that it creates light patterns on the clouds above. The pit’s water when green usually means high copper levels.

The Colorful Streaks on the Walls Are Alive

If you look at the pit walls, you’ll notice bright green and blue stripes. These aren’t paint or mineral stains, but tiny living organisms growing in groups called biofilms. They use special chemicals (bioactive secondary metabolites) that help them survive in conditions 10,000 times more toxic than the norm.

It’s a Wasteland

Tiny drops of toxic water blow from the pit’s surface. This has turned the area into a human-made wasteland that stands out sharply against Montana’s usual mountain greenery.

Around the edges of Berkeley Pit, you’ll find soil that contains so many metals (up to 1,000 times more than normal). As a result, plants can’t grow within 300 feet of the pit.

Toxic Water Transforms Objects

When things fall into the pit, the acid water changes them in strange ways. Metal objects quickly get covered in copper. Animal and plant material can turn into partial fossils as minerals replace their natural materials. Everything that goes into the pit gets coated with layers of minerals while keeping its original shape.

Managing the Toxic Water

Engineers use sensors all over the pit to watch the water level. A treatment plant works non-stop to clean 7 million gallons every day using lime and settling ponds to remove metals and acid.

The water must stay below 5,410 feet above sea level to prevent it from mixing with local groundwater. Power line poles descend the walls of the pit.

How to See the Pit Safely

Each year, more than 40,000 people come to see this unusual and dangerous place. There’s a safe viewing platform that sits 130 feet above the water where you can view the pit.

This spot gives you a clear view of the entire toxic lake while keeping you well away from danger. The platform has signs that tell you about the pit’s history.