Story : In the seventh episode of Superquark, the documentary: “Underwater with crocodiles”. The Nile crocodile dominates African waterways unchallenged. It is one of the largest and most feared reptiles on our planet. Since they are able to grab victims from the banks and boats, crocodiles terrorize the inhabitants of the villages with which they share the river. The naturalist operator Brad Bestelink is planning an incredible feat, he wants to dive into the waters of the Okavango Delta, to study these unpredictable creatures in their natural habitat. The goal is very ambitious. To erase the polio virus from the face of the Earth by 2013, to cause its extinction. This is the project of the World Health Organization that, for over 20 years, has been engaged in a relentless fight against an infectious disease that causes very serious paralysis and affects especially the youngest.