In the decade that fisherman Edward Njeleza has been trawling the deep, clear waters of Lake Malawi in Africa's Great Rift Valley, he has seen his once abundant catch shrink by 90 percent.

Now he spends most days on the shore searching for pods and a special type of grass he uses to make necklaces, key rings and bracelets to supplement his income.

In the past, he and his nine fishing mates would on average catch roughly 300 kilogrammes (650 pounds) of fish a day, but that haul has dropped to no more than 25 kilogrammes, he told AFP.

"We go fishing but never come back with much," said Njeleza, waiting by the lake with a bag full of homemade jewellery slung over his shoulder.

"And we don't catch big fish."

Lake Malawi, one of the deepest in the world, is estimated to have the largest concentration of freshwater fish species -- up to 1,000, according to the UN Scientific and Cultural Organisation (UNESCO).

And a local favourite, the Oreochromis lidole or "chambo" as it is known in this landlocked southeast Africa state where it is a vital source of protein for millions of poor, is among the hardest hit.

In its last study on chambo, the International Union for the Conservation of Nature estimated in 2004 that the population had declined 70 percent over the previous 10 years, William Darwall, head of the IUCN's freshwater biodiversity unit, told AFP.

Overfishing is the main cause, and scientists blame both a lack of government muscle to enforce seasonal fishing bans as well as environmental degradation.

"The primary reasons why the fish stocks, specifically chambo, are going down is overfishing, (and) degradation issues because of factors related to the effects of climate change," said William Chadza, director of the Centre for Environmental Policy and Advocacy in Blantyre, the country's finance and commerce hub.

Climate change is said to have affected rainfall patterns and caused a drop in the lake's water levels, also hit by the effects of deforestation on tributaries feeding the lake.

- 'Going towards a disaster' -

In Makawa fishing village near Mangochi town in the country's southeast, Njeleza has no choice but to diversify.

Apart from making jewellery, he hopes to bait the odd tourist visiting the lake into a ride in his blue and white boat, which he has named Wanangachi, meaning "What is the problem with us?"

At night he returns to fishing, but stays much longer than in previous years.

"We used to spend just about two hours out on the lake and come back with a boatload of fish -- now we need about 12 hours, and bring back less than before," Njeleza said.

Some officials fear chambo could face extinction in Lake Malawi.

"It's a very big issue, and I think if we don't do something ... we could be in a dire state shortly," Chadza told AFP.

But rangers say the fight to save the fish is a losing battle.

"We are not winning," said Gervaz Thamala, chief of the Wildlife and Environmental Society of Malawi.

Laws to protect the chambo exist, but "the major problem which we have is governance," Thamala said.

"It seems we are going towards a disaster, which is quite critical," he warned. "Extinction is also a possibility because we have not fully developed the aquaculture sector, which could act as a buffer."

Back at the lake, Dogo Morris leads a team of 10 fishermen pulling in their nets, cast six hours earlier, but their haul is only about 10 kilogrammes of fingerlings.

"I have nothing to sell today," he tells more than a dozen would-be customers, who walk away dejectedly clutching their empty bowls.

Fishmonger Raymond Johnson, who supplies hotels and restaurants in Blantyre, Malawi's largest city, has waited three days to purchase chambo, which he buys in bulk -- hundreds of kilogrammes per trip to the lake.

"My business is not doing well. It has gone down by 40 to 45 percent," said Johnson.

Back in Blantyre, restaurant owners share his despair, saying diners complain that the fish on their plates are getting smaller all the time.