From the air, Lake Victoria looks busy with fishing boats and markets.

But according to WWF, the fish populations that underpin this activity are shrinking fast.

The report, 'Africa’s Forgotten Fishes', has found that 26 percent of freshwater fish species across the continent are at risk of extinction.

That means one in four could be lost forever.

On the shores of Lake Victoria, fish traders are already living with the consequences of decline.

Elizabeth Didi has sold fish for decades.

She says: "Back in the days we would get like 200 kilograms per day and nowadays just getting 20 kilograms is a big challenge and now it seems like the numbers are going down. This is what I know for my life and if the number of fish goes down, I don't know what else I will go into."

Some fishermen are turning to cage farming, raising fish in enclosures in the open water to guarantee a harvest.

WWF warns that research on freshwater fish has been chronically underfunded compared with marine fisheries.

WWF says at least 170 fish species are critically endangered and 9 have already vanished.

More than 500 are classed as data deficient, meaning too little is known about them, but researchers warn that does not mean they are safe.

Eric Oyare, an environmental economist at WWF, explains: "The report established that we have over 500 species which are data deficient... being data deficient does not equal to not at risk."

He adds that pollution and invasive species are among the greatest threats.

"We are faced by invasions by non native species including water hyacinth and other aquatic species... We are also faced with pollution within our freshwater ecosystems especially within the wetlands and this is driven by industrial waste, pesticides and other chemicals... but also causes like mining which pollute these ecosystems."

Invasive species such as Nile perch and water hyacinth have altered the lake’s ecosystem.

Pollution from farming, mining and industry has poured chemicals into rivers and wetlands.

Rapid urbanisation around Kisumu is adding waste, while fertiliser run off has left Lake Victoria hypereutrophic, overloaded with nutrients that fuel algal blooms.

WWF warns that these problems are not unique to Lake Victoria.

According to the report, in southern Africa, catches in the Zambezi floodplain have dropped by 90 percent, while in Lake Malawi, stocks of chambo tilapia have fallen by 94 percent.

Also detailed in the report is that the Pagani halpo fish in Kenya is already officially extinct, while Lake Victoria itself has lost more than 200 of its 600 cichlid species.

Freshwater fish play a crucial role in recycling nutrients and maintaining healthy ecosystems.

They are also a major source of protein and income.

WWF is urging governments to adopt its Emergency Recovery Plan, which calls for cleaning up water, controlling invasive species, protecting rivers and ending unsustainable fishing.

At Kenya’s Marine and Fisheries Research Institute, scientists say overfishing is also a major problem. Senior researcher Nicholas Gichuru explains that illegal nets continue to land undersized fish.

Despite bans, illegal monofilament nets are still used on the lake.

These nets catch fish of every size, including juveniles before they have reproduced, leaving populations unable to recover.

He says that combined with nutrient pollution and rapid urban growth around Kisumu, the lake is under unprecedented pressure.

While markets like this one around Lake Victoria might seem busy, according to scientists the abundance they rely on is dwindling.

The report warns that the next decade will be crucial in deciding whether Africa’s inland waters continue to decline or can be restored.

AP video by Desmond Tiro