7 Days Great Migration Tanzania Safari to witness the largest herd movement of animals on the planet? With the great migration and also visiting the best national parks in northern Tanzania, this is the perfect itinerary for you. The focus during this trip will be on the western part of the Serengeti, where the Great Migration crosses the Grumeti River from June to October. The herds of wildebeest and zebra must outsmart the huge Nile crocodiles and fast-flowing water before facing predators waiting on the other side.