Bill Keveney | USA TODAY

PASADENA, Calif. — After years portraying the beloved denizens of Bikini Bottom, the voice actors behind "SpongeBob SquarePants" will be front and center as human versions of their characters as part of a 20th anniversary celebration for the hit series.

How did that feel? "It went from weird to really fun," said Carolyn Lawrence, who portrays Sandy Cheeks, during a Television Critics Association panel Monday.

Nickelodeon will commemorate the 20th anniversary of "SpongeBob," which premiered on July 17, 1999, with what it's calling the "Best Year Ever."

The celebration kicks off July 12 with "SpongeBob's Big Birthday Blowout," a new special mixing live action and animation and featuring the cartoon's voice cast playing human versions of SpongeBob, Patrick, Mr. Krabs, Sandy, Squidward and others.

David Livingston

(Another feature film, "The SpongeBob Movie: It's a Wonderful Sponge" is due in theaters in 2020.)

In the special, Patrick Star (Bill Fagerbakke) takes the characters to the surface world to distract them while birthday party plans are being made in Bikini Bottom. There, the voice actors portray slightly different versions of their characters, not with sponge or starfish costumes, but by wearing clothing and acting as human versions of their underwater doppelgangers.

They end up at a restaurant called the Trusty Slab, which sounds much like their watery hangout, the Krusty Krab. A brief clip showed Tom Kenny flipping burgers at a frenetic pace, much like his character, SpongeBob.

"It was like the most meta of meta moments ever," Kenny said, "walking into a place that looks quite a bit like the Krusty Krab and with people you've been in the (recording) booth with for 20 years, and they're all kind of dressed like their characters."

The terrestrial characters have slightly different names from their submerged counterparts, which was an adjustment for the actors.

Clancy Brown, who plays the cranky Mr. Krabs, "couldn't not call Rodger (Bumpass) Squidward," Fagerbakke said. "He's been calling him Squidward for 20 years."

Bumpass said he's had "the hardest time" explaining the live-action element to friends who are fans of the cartoon. "They didn't understand we were doing doppelgangers of our characters."

Kenny, however, doesn't find the sea/land transition that much of a shock.

"People were like, 'What's it like to be a live-action SpongeBob?' And I think I always have been. I think that's how I got the gig in the first place," he said. Creator Stephen Hilllenburg, who died last year, told him, "'You're talking like that guy. You want the job?'"

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Highlights from Television Critics Association