Lake Malawi, Malawi (CNN) -- Lake Malawi has more freshwater fish than anywhere else in the world, and park rangers are on the frontline of the battle to save them.
But Hastings Kawerenga, a ranger in charge of the Malawi government's conservation efforts in the Lake Malawi National Park, says he is losing the struggle to prevent illegal fishing.
A recent comprehensive study by the Intentional Union for Conservation of Nature (IUCN) found 21 percent of freshwater fish in Africa are threatened with extinction, putting the livelihoods of millions of people at risk.
The report highlighted Lake Malawi and said loss of species was particularly serious because so many people rely on the fish for food.
Because the majority of fish live in the shallow waters near islands, rangers have implemented a fishing ban within 100 meters of islands.
However, demand for fish is so high from local villages that Kawerenga's rangers have an uphill battle to persuade them to stay away from restricted waters.
Kawerenga told CNN: "The lake is the backbone of the economy for the people in this area. We have villages that started as fishing camps. They came from the North and settled permanently but solely for fishing.
"They don't understand and they don't support [the ban on fishing in the shallows]. The sense of ownership in them is too high. They look like the National Park grabbed their asset. It's a battle, it's a struggle."
Lake Malawi is a UNESCO World Heritage site and UNESCO says the lake's importance for studying the evolution of fish is comparable with finches in the Galapagos Islands.
Among the fish Kawerenga is trying to save is one kind known locally as "mbuna," or abroad as cichlids. Lake Malawi contains more than 400 species of the brightly colored fish, all but five endemic to these waters.
Another is known locally as "chambo." The IUCN report said: "In Lake Malawi, a group of fish, known as 'chambo' by locals, forms an extremely important source of food. Of these, Oreochromis karongae, an endangered species, has been hugely over fished, with an estimated 70 percent reduction in the population over the past 10 years."
When he discovers fishermen catching these species, Kawerenga sometimes confiscates nets.
He knows the fishermen in their dug-out canoes will continue to battle for a living on the lake, but is determined not to give up. He understands the implications of an empty lake.
"Then no tourists, no money, no employment -- we will lose a lot of things," said Kawerenga. "People are poor. They depend on the resources that we are protecting."
In the dry landscape surrounding Lake Malawi, there are precious few options.
Catriona Davies contributed to this report