Jeffrey Gettleman, New York Times, January 24, 2015

Out here on the endless swamps, a harsh truth has been passed down from generation to generation: There is no fear but the fear of hunger.

With that always weighing on his mind, Mwewa Ndefi gets up at dawn, just as the first orange rays of sun are beginning to spear through the papyrus reeds, and starts to unclump a mosquito net.

Nets like his are widely considered a magic bullet against malaria–one of the cheapest and most effective ways to stop a disease that kills at least half a million Africans each year. But Mr. Ndefi and countless others are not using their mosquito nets as global health experts have intended.

Nobody in his hut, including his seven children, sleeps under a net at night. Instead, Mr. Ndefi has taken his family’s supply of anti-malaria nets and sewn them together into a gigantic sieve that he uses to drag the bottom of the swamp ponds, sweeping up all sorts of life: baby catfish, banded tilapia, tiny mouthbrooders, orange fish eggs, water bugs and the occasional green frog.

“I know it’s not right,” Mr. Ndefi said, “but without these nets, we wouldn’t eat.”

Across Africa, from the mud flats of Nigeria to the coral reefs off Mozambique, mosquito-net fishing is a growing problem, an unintended consequence of one of the biggest and most celebrated public health campaigns in recent years.

The nets have helped save millions of lives, but scientists worry about the collateral damage: Africa’s fish.

Part of the concern is the scale. Mosquito nets are now a billion-dollar industry, with hundreds of millions of insecticide-treated nets passed out in recent years, and many more on their way.

They arrive by the truckload in poor, waterside communities where people have been trying to scrape by with substandard fishing gear for as long as anyone can remember. All of a sudden, there are light, soft, surprisingly strong nets–for free. Many people said it would be foolish not to use them for fishing.

“The nets go straight out of the bag into the sea,” said Isabel Marques da Silva, a marine biologist at Universidade Lúrio in Mozambique. “That’s why the incidence for malaria here is so high. The people don’t use the mosquito nets for mosquitoes. They use them to fish.”

But the unsparing mesh, with holes smaller than mosquitoes, traps much more life than traditional fishing nets do. Scientists say that could imperil already stressed fish populations, a critical food source for millions of the world’s poorest people.

Scientists are hardly the only ones alarmed. Fistfights are breaking out on the beaches of Madagascar between fishermen who fear that the nets will ruin their livelihoods, and those who say they will starve without them. Congolese officials have snatched and burned the nets, and in August, Uganda’s president, Yoweri Museveni, threatened to jail anyone fishing with a mosquito net.

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Many of these insecticide-treated nets are dragged through the same lakes and rivers people drink from, raising concerns about toxins. One of the most common insecticides used by the mosquito net industry is permethrin, which the United States Environmental Protection Agency says is “likely to be carcinogenic to humans” when consumed orally. The E.P.A. also says permethrin is “highly toxic” to fish.

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