Cartman's mom signs him up for swimming lessons at the South Park Community Pool. Stan and Kyle warn him that the first graders urinate in the pool and they turn out to be right. During his first lesson, Cartman is disgusted by the first grader pee.
Later in the episode, the pool is closed because the giant snake is wreaking havoc in South Park and all over the United States. Cartman takes the opportunity to go to the pool and manages to swim to the deep end, which is 9 1/2 feet deep. Once that happens, however, the pool reopens due to the giant snake being destroyed. The first graders reenter the pool and urinate, turning the entire pool yellow with pee. Cartman promptly leaves the pool in disgust.