S1, E4: Freshwater covers only a tiny fraction of the earth's surface, but it is a vital meeting place for many animals - the stage on which millions gather to find a mate. Yet with so little of it available, and often only briefly, the challenge for most individuals is how to overcome intense competition when your rivals are just as dependent on the precious freshwater for their success. Whether it is from melting ice, torrential rain or shrinking wetlands, the cycle of freshwater is the trigger for spectacular mating rituals and fierce combat. The start of the rains in South Africa triggers a violent battle between male giant African bullfrogs. Rare hooded grebes in Patagonia perform one of nature's more comical dances to seduce their partner, and a male cichlid fish builds a home for his harem from old snail shells, but a sneaky dwarf has the last laugh there. The mating season for animals that live in freshwater is often determined by when is best for their new offspring - even if that moment is far from ideal for the parents. In the wetlands of Zambia, female lechwe antelope search for the strongest males while contending with drought, and in the Pantanal of Brazil at the end of the dry season, caimans congregate in huge numbers around the last remaining water to perform their spectacular displays. For all those dependent on the cycle of freshwater to breed, timing is everything.