This is one of the most scenic moments of the Great Migration to be experienced at least once in lifetime.
The crossing of a river is a very critical moment for the herds as it entails many hazards and there are several aspects to be taken into account.
Firstly, it is essential to choose the right spot where to cross; it is very important to make sure that there are no predators lurking on the banks, probably hidden behind trees or shrubs, for this reason the wildebeests choose banks without vegetation.
They have to look for the least steep banks, this applies especially for the Mara River that features high sand banks, as the animals risk to break a leg down, and also those that are easy to climb on the opposite bank.
Other important aspects to be verified are primarily the water depth to avoid the risk of drowning, the presence of large rocks in the river bed that could be a further obstacle to the crossing and the water current that could drag the animals away.

Last but not least it is the fact that the river hides one of the most ruthless predators: the Nile crocodile.

Crocodiles stay under the water surface awaiting for the crossing and when herbivorous enter the water, they jump out incredibly quickly and catch them, but often they eat wildebeests and zebras who failed to cross and drowned.
The crossing of the Grumeti River and the Mara River is somewhat different.
The herds usually arrive at the South bank of the River Grumeti in June and flock here reluctant to cross; when the space on the bank inevitably becomes too small for all the animals, wildebeests and zebras are forced to cross  the river and move to the Northern grasslands, from where then they will head Northwards to the Mara River and the evergreen pastures.
By this time of the year the Grumeti River has little water and it is not difficult to cross, the main risk lies with the presence of Nile crocodiles that have waited for the arrival of the migrating animals for months.
The crossing takes place only once because the river is right along the trail covered by the herds on their way to the North and occurs in a week or two, so it's not easy to be on spot at the right time.
The event is undoubtedly highly dramatic because the herds cross the river together and you can see everywhere animals plunging into the water in great leaps, trying to avoid obstacles and reach the opposite bank as quickly as possible, before being able to rest in the Ruwana plain.
The situation at the Mara River is quite different.
First, the Mara is much wider and has a higher flow rate than the Grumeti and its banks are steep and sandy, this all makes the crossing much more difficult.

On one hand the river has many meanders and the herds cross it from different points several times a year; on the other, since the herds remain in Northern Serengeti and the Masai Mara for 3 or 4 months, they keep on moving in their wanderings and they often encounter the Mara on their way.

Sometimes the herds flock in great numbers on one bank for days, watching the river to find the optimal point to cross, undecided about what to do and, when the first animals begin to cross, the others follow them irrationally, almost blindly, just trusting the animals preceding them.
Sometimes is a bulky crossing like the one occurring at the Grumeti River, other times the wildebeests ordered rows at the mercy of the force of the river waters, with the looming threat of the Nile crocodiles in the water and land predators on the banks.
It is relatively easier to view the crossing of the Mara River than of the Grumeti River because there are more opportunities; one thing for sure is that the wildebeests sometimes take days to make the decision to cross.

Where is possible to spot the crossing of the herds of Great Migration

Western Corridor: this encompasses the Grumeti River area, the Musabi and Mbalageti plains to the South of the Grumeti River and the Ruwana plain to the North of the river; these are the areas where in June it is most likely to view the crossing.
Serengeti Mara and Masai Mara: from July to October, this is where you can view the crossing of the Mara River by the herds as they search for new pastures and follow the rare rainfalls; though you need a bit of luck to find the right position. 

The position by journey stages is characterised by the following events

  • The birth and weaning of puppies
  • The start of the journey
  • The mating season
  • The crossing of the Grumeti River and the Mara River
  • The growth of puppies and new pregnancies
  • The return to the Southern pastures

Great Migration through Serengeti National Park Map - Illustration Credits: Marco Dal Molin -