Dear EarthTalk: Which are the most fuel-efficient hybrid and/or all-electric cars available to consumers today (just the affordable ones, please!)? -- Jack Madison, Chicago

Given increased environmental awareness, high gas prices and a continually slumping economy, it's no wonder that more fuel efficient cars are all the rage these days. The best deal going may be Honda's hybrid, the 42 miles-per-gallon Insight ($18,350). Meanwhile, the newest version of Toyota's flagship hybrid, the Prius ($23,015), garners an impressive 50 mpg. Other solid choices include Toyota's 41-mpg Camry hybrid ($25,900), Ford's 39-mpg Fusion hybrid ($28,700), Lexus' 42-mpg CT 200h ($29,120) and Lincoln's 39-mpg MKZ Hybrid ($34,755).

For even greater efficiency and lower sticker prices, consider going electric, whereby you can charge your vehicle at ordinary electric outlets at home or work. Mitsubishi's new MiEV ($29,125) electric is the most fuel-efficient car available to U.S. consumers in the 2012 model year, achieving 112 "mpg-equivalent" (the U.S. Environment Protection Agency's rating for electric vehicles that swaps in electricity for gas in its calculations) and a 62-mile range per full charge -- not bad considering four adults can fit fairly comfortably inside. Another option is Smart's FourTwo Electric ($28,752), a two-seater with an 87 mpg-equivalent. And Nissan's all-electric Leaf ($35,200) achieves 99 mpg efficiency for a range up to 100 miles.

So-called "plug-in" hybrids also allow drivers to charge their vehicles' electric batteries via common power outlets, but also can use gasoline as needed for a longer range. Though pricey at $39,145, the Chevy Volt may save you money in the long run because it gets a whopping 94 mpg-equivalent in its preferred all-electric mode. An onboard gas generator produces more electricity as the vehicle is driven, extending the car's range with a full tank of gas to some 375 miles. Toyota released a plug-in version of its Prius ($32,760) this year, as well. It gets 87 mpg in electric mode (but this will only get you 15 miles without gas assistance) and a respectable 49 mpg in regular hybrid mode.

Contacts: DOE's Fuel Efficient Vehicle Tax Information Center, www.fueleconomy.gov/feg/taxcenter.shtml; DSIRE, www.dsireusa.org; Edmunds' "Decoding Electric Car mpg," www.edmunds.com/fuel-economy/decoding-electric-car-mpg.html.

Dear EarthTalk: How is it that dams actually hurt rivers? -- Missy Davenport, Boulder, Colo.

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Dams are a symbol of human ingenuity and engineering prowess -- controlling the flow of a wild rushing river is no small feat. But in this day and age of environmental awareness, more and more people are questioning whether generating a little hydroelectric power is worth destroying riparian ecosystems from their headwaters in the mountains to their mouths at the ocean and beyond.

According to the non-profit American Rivers, more than 1,000 dams across the U.S. have been removed to date. And the biggest dam removal project in history in now well underway in Olympic National Park in Washington state where two century-old dams along the Elwha River are coming out. But why go to all the trouble and expense of removing dams, especially if they contribute much-needed renewable, pollution-free electricity to our power grids?

The decision usually comes down to a cost/benefit analysis taking into account how much power a given dam generates and how much harm its existence is doing to its host river's environment.

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