The show, which stars extreme angler and biologist Jeremy Wade, has been renewed for a second season, which is set to start filming shortly for a spring 2010 premiere. The new episodes will explore more killer fish in freshwater locales across the globe, including several in the United States, the network said in a release.
The first season of "Monsters" averaged more than 1 million households across its seven premiere episodes, making it the best-performing series in network history, Animal Planet said.
Last Sunday's season finale, "Freshwater Shark," was watched by about 1.47 million viewers.
Animal Planet said it plans to air a nine-hour marathon of "River Monsters," featuring all seven episodes, plus a never-before-seen, two-hour special cut of "Killer Catfish," on May 31.
"'River Monsters' was a ratings monster, and we're excited to send Jeremy back into the murky depths to explore more stories," Marjorie Kaplan, president and general manager of Animal Planet Media, said in a statement. "With over a million viewers gripped to their seats every week, Animal Planet is delivering on our promise of break-through television."