Lake Tanganyika - Saving the World’s Largest Tropical Lake

“You stick your head in the water, and it’s like a Dr. Seuss book down there.” - Craig Leisher , The Nature Conservancy in Africa Portfolio Director

Almost 13 years ago on a windy day, a boat carried a group of The Nature Conservancy scientists across Lake Tanganyika for the first time. They splashed ashore at the feet of the Mahale Mountains, home to Tanzania’s largest remaining population of chimpanzees. Craig Leisher was on that expedition, helped design the Tuungane Project, and has played a leading role ever since. Now that we’re expanding our work on this amazing lake, we’ve asked Craig to tell us about it.

What makes the lake special?

Lake Tanganyika is a lake of superlatives. It’s the longest in the world at 673 kilometers, and the second-largest by volume. It’s also the world’s oldest and deepest tropical lake. Its walls drop off dramatically: You can be 5 kilometers offshore and the lake bottom is 1,000 meters below you. From a biodiversity standpoint, it’s extraordinary. It has more genus-level aquatic diversity than any other lake in the world. We’re not talking about species-level diversity; we’re talking genus level! Most of the species are in the cichlid family—about 250 species of cichlids, in fact—but over the last 10 million years, these have diverged into so many different shapes and colors that they warrant their own genus.

How can a lake this large, this deep, be vulnerable?

Many of the fish species breed in the sunlit shallow areas near shore, and this makes them easier to catch. Catching fish before they breed is a sure way to crash a fishery. In fact, it’s in the top 10 meters of water where you find most of the life in the lake—that we know about. Who knows what’s in the blue-black depths of this lake!

Pollution in this lake can linger for centuries: The estimated “residence time” for water in Lake Tanganyika is 5,555 years. That’s how long it takes a drop of water that enters from, say, the Malagarasi River, to when that drop leaves by the only exit: the Lukuga River, which flows into the Congo River.

Why should it be a conservation priority right now?

We know that in terms of species diversity per unit area, freshwater ecosystems have more diversity than marine ecosystems or terrestrial ecosystems. We also know that freshwater fish have the highest extinction rates of any vertebrates. Within freshwater fish, cichlids have the largest number of endangered species, so how could we not prioritize the global bull’s-eye of genus- level cichlid diversity? It is one of the top freshwater conservation priorities in the world.

Read more in our Africa Year in Review 2023: https://www.nature.org/content/dam/tnc/nature/en/documents/Africa-YIR-2023-Web-Final.pdf