The Fatlands is episode 33b from season 3 of Rocko's Modern Life. In this episode Rocko tries to help Spunky to lose weight that he has recently put on. Bloaty and Squirmy return travelling to newly discovered lands due to Spunky's weight gain with a western theme.
Inside Spunky's fat, furry body, Bloaty is shown watching fishing shows on television when Squirmy shows up and the intro of the two parasites is shown. After the intro, Squirmy asks Bloaty how life is, to which Bloaty responds that he is sick of it since it's mundane and repetitive. Squirmy shows him a newspaper of a new land discovered and opportunities required as well. So Bloaty and Squirmy decide to pack up to move to the western side.
Meanwhile, Rocko notices that Spunky has gained a lot of weight and attempts to get him diet dog food. Inside of the dog, Bloaty and Squirmy come across a western town called Tickle Flats, where a bug attempts to suck through the skin, causing the dog to scratch it away (which the parasites call it as a "clawvalanche). The two friends decide to go around.
Later, Rocko tries to take Spunky out for a walk, but the dog staggers around the floor of the living room. Back inside the fat dog, Bloaty and Squirmy come across another town called Scapstone, where they are offered jobs as sheriffs of the city.
Rocko and Heffer are then seen dragging Spunky outside and come across a weight-loss clinic called Buff-Pooch, where they take him to meet Dr. Hutchison, who is now a canine nutritionist. While she examines Spunky, Bloaty and Squirmy are seen getting a drink in the Bucket-O-Pus bar, where the bartender warns them about The Blood Brothers, mosquitoes who hate lawmen. The Blood Brothers show up and give out a dance. After the dance, they threaten to run Bloaty and Squirmy out of town if they don't leave by noon, prompting the two friends to run away. But their time is up (since it's daylight savings time and the clocks have been set an hour back) and are taken as hostages.
At the weight-loss clinic, Spunky is given many tactics to losing weight, and inside his body, the Blood Brothers attempt to spray Bloaty and Squirmy. But their attempt becomes inhibited when they are asked by Squirmy, who notices that they are in Tickle Flats, to perform their dance again. This causes Spunky to get irritated by this and he scratches himself, which causes his paw to scratch away the Blood Brothers.
Meanwhile, Dr. Hutchison tells Rocko that Spunky has not lost any weight at all and says that it is time to resort to liposuction. Inside the dog's body, Bloaty and Squirmy are tired and dehydrated while trying to stagger through the middle of nowhere. When they discover that the Fatlands had disappeared, their city returns and they are back in their own town. Bloaty tells Squirmy that he would much rather revert to his mundane life and repeat.
Meanwhile, Spunky is revealed to be very skinny and Dr. Hutchison tells Rocko that the dog shouldn't have any fatty foods or eat between meals, as well as giving him a bag of Spunky's fat. Rocko asks Heffer to carry the bag of fat for him as they walk home. When Rocko asks Heffer what he wants to eat, Heffer tells him that he isn't hungry anymore and he belches off-screen, implying that he has devoured the entire bag of Spunky's fat.