When the Grumeti River obstacle has been taken, the herd moves further north and starts crossing the next big hurdle, the Mara River, in July or August. The Mara River crossing is where so many iconic Great Migration photos have been taken. After this crossing the herd flocks to the northwest plains and Masai Mara National Reserve in Kenya. The August – September period is considered being a bad time to visit Serengeti National Park and see the Great Migration as the herd moves into the Masai Mara in Kenya. However, migration patterns show that about half of the herd stays on the Tanzanian side, in the Mara Serengeti area. In this period, smaller herds of wildebeest (well consider small… herds may count up to between 500 and thousands of individuals) frequently cross the Mara River, back and forth, for no apparent reason. This is an excellent time to stay at one of the Serengeti Mara camps.