Most Americans have the luxury of believing that the effects of climate change lie in the future. After all, our houses are not crumbling into melting permafrost, as in Alaska, or the rising sea, as in the Maldives. We have enough water to grow food, unlike millions around the world. And we have drinking water for all, unlike nearly 1 billion other people.

But just because most American drinking water is technically safe for humans does not mean it’s safe for everyone else. About 40% of American rivers are not clean enough for fishing or swimming, according to the EPA. One of those rivers flows in my Colorado backyard. It’s the Upper Snake River, at the very tippytop of the Rockies. This is a tributary of the Snake River, which flows west into the Blue River and then the Colorado River on its way to the Gulf of California.

The Upper Snake River is unusual. Though it lies west of the Continental Divide, much of its water is diverted east, piped from the Dillon Reservoir by a tunnel under the mountain and east to the city of Denver.

The Snake River is not safe for fish. The fish that do live there have to be restocked regularly. Why? Because the concentrations of heavy metals are too high. And they’re rising. Fast. Concentrations of zinc are 4 times higher than they were in 1980.

Environmental scientists think climate change is the culprit. I spoke recently with Caitlin Crouch, a grad student in environmental studies at the University of Colorado. She explained that they think the problem starts with a too-early spring:

Snowmelt is happening two weeks earlier than it did thirty years ago.

This in itself startled me. I had no idea the seasonal change was that dramatic.

Probably because of the earlier snowmelt, the water is becoming more acidic.

Why? Because of pyrite, a naturally occurring mineral, often called fool’s gold.

When pyrite weathers, it turns into sulfuric acid and iron in water, which further dissolves the rocks around it, leading to more acidity.

Possibly because the ground is drier or because the water table is lower and water is finding new flow paths, it is picking up the minerals and acids, which leads to more weathering of rock, which leads to greater acidity in the water.

Here is Caitlin with some friends at the place where the Upper Snake joins Deer Creek. This spot is just downstream from where zinc levels have increased fourfold in the last thirty years. Note the gray-colored streambed on the left. This is aluminum precipitating out of the water, which has a lower acid level than the water on the right. The red is iron oxide, which precipitates onto the streambed because of the higher acidity of the Snake River:

The process we’re talking about is the same one that leads to acid mine drainage and the problem of toxic runoff from old mining operations. Except that these are naturally occurring minerals, and the process is happening not because of mining, but because of climate change.

Here is a photo of acid mine drainage. Caitlin says the naturally occurring process looks the same.

One issue with the naturally occurring acid water is that it complicates any cleanup from acid mine drainage. For example, as Caitlin asks,

What if you put millions of dollars into acid mine runoff cleanup, and in twenty years the fish are dead again? This may make cleanups more complicated.

At the present time there is no threat to Denver’s drinking water. By the time the acidic water heads down the hill, the heavy metals have dispersed. Acidity and heavy metal levels are within legal limits.

But I wonder about the future. If climate change continues to increase, will this acid water runoff become more widespread? Is it happening in other places now? Caitlin and her team are expanding the scope of their studies to see if they can find the answers to these questions.

In the meantime, I think it’s a leading indicator of climate change that should give us pause. We have not just ourselves but all the other creatures to think about. Are we content when 40% of our streams and rivers are not safe for fish (or us)?

What you can do:

1. Work to reduce climate change. You know the drill. The big three that individuals can do are:

• Drive less.
• Fly less.
• Eat local.

2. Work for solutions beyond fossil fuels. Here are some organizations that would be happy for your help:

• 350.org
• Transition Colorado (Update: name later changed to Local Food Shift)
• Grist.org

3. Work for clean water for everyone—fish too.

• Donate to American Rivers or to water.org or to other water-saving organizations.
• Fundraise for safe drinking water.

For more information:

• Caitlin Crouch is part of a research team led by Diane McKnight of the University of Colorado Environmental Engineering Program.