The Tardicaca Shark, is a fictional fresh water shark species, which is found in Lake Tardicaca. The Tardicaca Shark only appeared in the episode "Crippled Summer", where it was seen having intercourse with Nathan twice. The incident is frequently brought up by Mimsy, much to Nathan's fury.
The shark's shape and size appears is similar to a Great White shark. They share the same shaped fins and head, as well as teeth and eyes. However, it has brown/green skin and nasial barbels similar to those of a catfish. It purportedly has a 9-inch penis, much to Nathan's chagrin.
Tardicaca Shark made a return in South Park: The Fractured But Whole DLC Bring the Crunch. It serves as a possible prey in fishing, and a requirement for the badge.
When The New Kid successfully catch the shark, Nathan will urge the New Kid to destroy the shark for him. It seems that Nathan can never forget about the shark.