What’s Worth Watching: ABC’s ‘Greatest Hits’, ‘Killing The Colorado’ on Discovery, ‘Ice Road Truckers’ on History and more.

Greatest Hits (9/8c, ABC): After celebrating musical pop nostalgia in five-year segments, this summer series wraps its season with a live two-hour blowout covering the entire quarter-century period from 1980 to 2005. Highlights include Celine Dion performing her chart-topping Titanic anthem “My Heart Will Go On” from Montreal, Ariana Grande tackling Whitney Houston standards, Adam Lambert channeling George Michael’s “Faith” and Flo Rida delivering a tribute to hip hop.

Killing the Colorado (9/8c, Discovery): The Discovery Impact series, which focuses on environmental issues and challenges, employs five Oscar-winning documentary filmmakers to investigate the political, economic and drought-related factors that have resulted in the severe depletion of the Colorado River, endangering the water supply to much of the West.

Ice Road Truckers (10/9c, History): Climate change takes a toll on the truckers as a 10^th season revs up, with warmer temperatures causing roads to open late and close early, adding to the pressure to deliver supplies in Canada’s North through the most grueling conditions.

Inside Thursday TV: Can’t wait for the Olympics’ Opening Ceremonies on Friday? NBC offers a prime-time preview special (8/7c), with Bob Costas hosting an overview of Rio—presumably the good and bad aspects of the embattled city—and featuring star Olympians including Michael Phelps, Kerri Walsh Jennings, Usain Bolt and the U.S. women’s gymnastics team. … Repeat of the night: The CW’s DC’s Legends of Tomorrow (8/7c) goes all Western as the team hides out among outlaws, with Jonah Hex (Johnathon Schaech) coming to the rescue.