Tropical Rivers: How Are They Different?

The Mara River is found in the tropics fairly near to the Equator. The tropics are a climate zone flanked between the Northern Tropic of Cancer to the Southern Tropic of Capricorn. These latitudinal lines, approximately 23 degrees north and south of the Equator, mark the place in both the northern and southern hemisphere where the sun appears directly overhead during one of the two annual solstice events. This zone has approximately 12-hour days and does not experience snow.

Tropical rivers differ from temperate rivers in several important ways. They tend to have higher water temperatures, greater biodiversity, more variable flow regimes tied to wet and dry seasons, and stronger connections between terrestrial and aquatic ecosystems. The Mara River is no exception — it supports a remarkable diversity of fish, amphibians, reptiles, birds, and mammals, including the famous hippos and crocodiles of the Mara.

The seasonal variability of the Mara River is particularly important for the wildebeest migration. The dramatic river crossings that occur during the dry season, when the wildebeest must cross to reach greener pastures in the Maasai Mara, depend on the Mara being one of the few perennial rivers in the region. Changes in the river's hydrology — whether from climate change, upstream water development, or land-use change — could have cascading effects on the entire Serengeti-Mara ecosystem.