The Los Angeles River in 2013. Engineers turned it into a narrow concrete channel in the 1940s, after a flood destroyed homes and left 100 people dead in 1938. Steve Lyon/Flickr hide caption

itoggle caption Steve Lyon/Flickr

A worker installs solar panels atop a government building in Lakewood, Colo. The industry has added more than 80,000 jobs since 2010, according to The Solar Foundation. John Moore/Getty Images hide caption

itoggle caption John Moore/Getty Images

Cruden ranks the Gulf oil spill as one of the most significant environmental disasters of our time. It "deserves ... all of our energy to make sure nothing like this ever happens again," he says. Gerald Herbert/AP hide caption

itoggle caption Gerald Herbert/AP

The city of Des Moines, Iowa, sits on the Raccoon and Des Moines rivers. The city's water works says it will sue three neighboring counties for high nitrate levels in these waterways. iStockphoto hide caption

itoggle caption iStockphoto

The elusive Kraken wasn't seen in its natural habitat until Dr. Edith Widder came up with some innovative technology. Kraken Attack by Ben Wooten/Used with permission of Paizo Publishing hide caption

itoggle caption Kraken Attack by Ben Wooten/Used with permission of Paizo Publishing

An excavator loads a truck with oil sands at the Suncor mine near the town of Fort McMurray in Alberta, Canada in 2009. Environmental groups that oppose oil sands mining have pointed to delayed and canceled projects as a sign of recent success. Mark Ralston/AFP/Getty Images hide caption

itoggle caption Mark Ralston/AFP/Getty Images