National Geographic Society

We don't see or hear them, but every day they quietly go about their work--filtering and cleansing our rivers and streams. And if we don't act soon, they'll disappear from the workforce just when we need them most.

One mussel alone can cleanse as much as a gallon of water per hour. Add up the work of a whole mussel community, and you get a virtual water treatment plant.

According to Ethan Nedeau, an expert on the freshwater mussels of New England, even half the population of mussels at work in a one-half mile segment of New Hampshire's Ashuelot River can help cleanse more than 11.2 million gallons of water a day--roughly the quantity of household water used by 112,000 people.

The United States ranks first in the world in the number of known species of freshwater mussels--292, compared with just 10 in all of Europe. But we're losing these "living filters" all too fast.

Today 69 percent of U.S. freshwater mussel species are to some degree at risk of extinction or already extinct. The most diverse assemblage of freshwater mussels ever known was located in the middle stretch of the Tennessee River in northern Alabama. Before the damming of the river in the early 1900s, 69 mussel species had been spotted in this reach; 32 of them have apparently disappeared, with no recording sightings in nearly a century.

My favorite freshwater mussel is the orange-nacre mucket (Lampsilis perovalis), found only in the rivers and streams of Alabama's Mobile River basin. Like many freshwater mussels, the orange-nacre mucket has a fascinating life cycle and exhibits some of the most sophisticated mimicry in the animal kingdom.

The females essentially use their offspring to lure fish into helping them colonize new stream bottoms. They package their larvae at the end of jelly--like tubes that can extend eight feet out into the water. To fish swimming by, the larvae dancing in the riffles of the river current looks like a tasty minnow. When the fish bites, the tube breaks, releasing the larvae into the stream. A few of the offspring attach to the fish's gills and hitchhike around with their finned host for a week or two, absorbing nutrients and growing along the way. Finally, the young mussels drop off, float to the river bottom, and colonize new territory--and before long begin their vital task of water purification.

Along with 16 other threatened or endanged mussel species in the Mobile watershed, the orange-nacre mucket is at risk of extinction---in large part due to excessive pollution and dams that have diminished the river habitat they need to survive.

To me, the loss of such industrious, fascinating creatures diminishes more than our water quality--it diminishes our natural heritage and our world.

Only habitat improvements, in some cases combined with mussel breeding and release efforts, can save these and the other 200 freshwater mussel species at risk nationwide.

So as we celebrate World Water Day, I hope we also celebrate the freshwater mussels that help keep our waters clean and healthy--and commit to efforts to conserve them.

Because I bet we'll miss these little creatures with the whimsical names when they're gone.

Sandra Postel directs the independent Global Water Policy Project and lectures, writes, and consults on international water issues. She is also Freshwater Fellow of the National Geographic Society, and serves as lead water expert for the Society's freshwater initiative. Postel is the author of several acclaimed books, including Last Oasis, which appears in eight languages and was the basis for a 1997 PBS documentary, and is co-author, with Brian Richter, of Rivers for Life. Her essay "Troubled Waters" was selected for Best American Science and Nature Writing. From 2000 to 2008, Postel served as visiting senior lecturer at Mount Holyoke College, and later in that term as director of the college's Center for the Environment. Postel is a 1995 Pew Scholar in Conservation and the Environment, and in 2002 was named one of the "Scientific American 50" for her contributions to water policy.

As I perused the bountiful wares of Rexville Grocery in rural Washington State last week, I was surprised to see a sign in their front window advertising an electric-vehicle charging station.

The small market and community center (which, at this time of year, offers delectable pies with berries plucked right from the surrounding farmlands) sits in the heart of the fertile Skagit Valley, about 60 miles (about 97 kilometers) from Seattle.

The concept of a country-store charging station spurred me to look into how mainstream electric cars—already popular in Europe— are faring in the U.S.

Hybrids have long been hot, of course—for instance, much has been made recently of the newly released third-generation Prius, which features integrated solar-powered technology.

For electric vehicles, it seems they are just on the cusp of going mainstream. I found the handy Plug-in Vehicle Tracker on Plug-In America's Web site, which maintains a list of most companies developing new electric vehicles.

According to the tracker, only two electric cars are now widely available in the U.S.: Commuter Cars's tiny Tango T600 EV, a two-passenger commuter car that sells for about U.S. $108,000, and the Tesla Roadster, which also carries a $100,000-plus price tag.

There's apparently a healthy electric car demand among the high-end crowd: Just today, Tesla opened its first East Coast dealership in New York City.

But one of most affordable cars in the pipeline seems to be TH!NK city, a compact electric car that can travel up to 112 miles (about 180 kilometers) on a single charge. It will have recyclable plastic body panels and a fully recyclable interior for a low carbon footprint.

It's produced by Think, a Norwegian car manufacturer that announced it would begin building a manufacturing plant in the U.S. this year, with a starting annual capacity of about 16,000 cars.

"The U.S. is quickly overtaking Europe as an attractive market for [electric vehicles], and is an ideal location to engineer and build EVs," Think CEO Richard Canny said in a statement.

A limited number of model and demonstration TH!NK cars will be available in 2010 (no starting price is listed on their Web site), but the Gas 2.0 blog says it won't be until 2011 that we'll be able to get one.

But if the plug-in tracker is any indication, we're going to be inundated with electric vehicles by 2013, including several new Chrysler models, Chevrolet's Volt PHEV, the Ford Focus EV, and more.

So go find that charging station near you.

--Christine Dell'Amore

Related:

--How green is your road trip?

--Have an eco-savvy summer with these tips.

Photograph courtesy Think