The citizens of Washington D.C. are using a time-tested method aimed at both changing their own behavior and providing funding for a good cause. It’s called a tax.

December is the last month that shoppers in the nation’s capital can pick up plastic or paper carryout bags for free. In January, a nickel surcharge will apply to all disposable bags from food and liquor stores.

To prepare retailers and the public for the new fee, Washington Mayor Adrian Fenty has launched the District’s “Skip the Bag, Save the River” education campaign.

The river he’s referring to is the Anacostia, which I would guess is as in need of cleaning up as any other river flowing past a major urban center in the Eastern United States. If you don’t think cutting down on throw away bags won’t make a difference, try this little experiment. Starting now, time how long it is before you use and throw a plastic or paper bag of some kind. Bet it’s more likely to be a matter of minutes or hours rather than days or weeks. Now multiply that by a few hundred thousand people and imagine the mess, a good portion of it ending up in rivers and other waterways.

If you live in the area, CVS and Safeway will be distributing free reusable bags in January when Washington’s law takes effect.