Nickelodeon

Cariba Heine, Claire Holt and Phoebe Tonkin star as regular teens on land, mermaids in water in Nickelodeon's "H2O."

H2O

7:30 p.m. on Nickelodeon

This live-action series follows three teens who appear ordinary on land but become mermaids once they hit the water. Filmed on location in Queensland, Australia, the show stars Cariba Heine, Claire Holt and Phoebe Tonkin as 16-year-olds who must keep a secret that is vulnerable to rainstorms and pool parties.

Next Big Bang

8 p.m. on History Channel

Decades of planning and construction culminate in a $10 billion experiment that may help explain why the universe exists. This special tracks the back story of the Large Hadron Collider (LHC), built to re-create the events thought to have taken place immediately after the big bang. The program also follows the experiment itself, which takes place in a 17-mile tunnel in Europe.

I Can Make You Thin

9 p.m. on TLC

Paul McKenna, who has helped celebrities get into shape, shares his anti-diet mentality in this five-part weekly series. McKenna points to scientific research and behavioral strategies viewers can implement at home to shed pounds without having to count calories. The program is inspired by the British version of McKenna's series, with a focus on his "4 Golden Rules," designed to change dieters' views of food.

-- The Washington Post