Las Vegas' overall ambience, not to mention those jug-sized cocktails, tends to breed a certain lasciviousness among its human inhabitants and visitors. Turns out that the same lust is infecting the mollusks of southern Nevada. Quagga mussels invaded the East and Midwest before hitching their way westward on promiscuous boats, and they were discovered in Lake Mead, outside of Vegas, just last year. The tiny Eurasian mussels are known for their hyperactive libidos and rapid-fire reproductive rates (1 million little buggers a year), but scientists recently discovered that the Lake Mead population seems to have been swimming in Viagra: They're reproducing three times as fast as other populations. (Researchers blame warmer water and other factors, not pharmaceuticals obtained on the Internet.)

Just a year after the reservoir's first quagga was seen, the mussels have made a mess of things. Bureau of Reclamation officials expect to spend some $1 million annually to keep the critters from clogging up pipes in Hoover Dam. Ecologists believe the mussels may have an unprecedented impact on the region's aquatic ecosystems. During the last year, quaggas have spread along the lower Colorado River and to other parts of California. The westward urge appears to be a family affair: Zebra mussels, cousins of the quagga, were also found in California and Colorado in January, marking the first time they've traveled west of the Continental Divide.

Mussels may be the least of Lake Mead's troubles. Scripps Institution of Oceanography researchers recently gave Lake Mead and Lake Powell a 10 percent chance of being functionally empty by 2013, and a 50 percent chance that "live storage" will be gone by 2021. It's just the latest blow to the Bureau of Reclamation's much more optimistic forecasts upon which the most recent Colorado River agreement was based.

During a year like this, it's hard to blame the Bureau for thinking that the Colorado will keep rollin' along forever. Snow has pummeled the Colorado River Basin since December, much to the chagrin of forecasters, who thought that a strong La Niña weather pattern would intensify the drought. Some Colorado communities have been cut off from the outside world for days due to heavy snow and avalanche danger. Ski areas are flush, but buildings have collapsed under the weight of snow. And 32 people have died in avalanches so far, including three in the mountains that border Los Angeles, which had just come off its driest year on record. The giant natural reservoir of the Rockies - otherwise known as the mountain snowpack - is now filled to the brim: The Upper Colorado River Basin has 25 percent more snow than the average for this time of year. Nevertheless, parts of Nevada, California, Utah, Wyoming, Idaho and Oregon remain in a drought, according to the U.S. Drought Monitor.

All that snow apparently makes ski areas want to stretch out a bit. County commissioners in Teton County, Wyo., gave Grand Targhee Resort - the lower-key, Idaho-side-of-the-mountains cousin of the Jackson Hole ski area - the go-ahead to expand after three years of wrangling. Targhee can now add 450 lodging units to its current 96, expand its commercial space and annex 120 more acres. The approval didn't come without controversy. Len Christensen, the lone commissioner opposed to it, told the Jackson Hole Guide, "We are going to change that whole area. I don't know how many people in 20 or 30 years are going to applaud the work we've done."

Backcountry skiers and enviros are booing Breckenridge Ski Resort's plan to increase its terrain by 450 acres. Ski area officials say the expansion will ease congestion on crowded slopes, while environmentalists and lift-shunning skiers argue that it would take some of the most valuable undeveloped terrain in the area and put it under the skis of lift-riding, fur-clad resort hounds. Other expansions are already under way or being considered across Colorado and in Oregon. Perhaps the most controversial is the Village at Wolf Creek in southern Colorado, which isn't technically a ski area expansion (the ski area's owners oppose it), but a proposal for a massive development next to the existing ski area. Environmentalists sued the U.S. Forest Service for approving a road to the development, and on Feb. 20, that lawsuit was settled: Now, the agency has to redo its environmental impact statement, which could significantly delay progress on the development.

Bridge over troubled highway

Wild animals in Colorado's White River National Forest might soon have a vegetated overpass to help them cross Interstate 70, a busy highway one expert calls "The Berlin Wall for Wildlife."

The 4 feet of soil on the "green bridge" over Vail Pass would be planted with native trees, shrubs and grasses to make the structure more attractive to cautious critters. Many species, including the threatened Canada lynx, are killed as they cross the highway between Eagle's Nest Wilderness to the north and the Holy Cross Wilderness to the south. Habitat connectivity is key to protecting wildlife populations and promoting genetic diversity, ecologists say.

"People are asking for an innovative highway system that respects the wildlife, the environment, and the community, and this bridge represents that," says Monique DiGiorgio of the Southern Rockies Ecosystem Project.

There's good news for drivers, too. Studies in Banff, Alberta, found motorist collisions with wildlife declined by about 80 percent after a similar structure was built.