China battles algae-choked lakes with fish

In Israel, the use of silver carp and other filter-feeding fish in drinking water reservoirs has worked in some cases, and failed in others, says Ana Milstein, an aquaculture expert there.

Others are more skeptical.

China's undertaking "sounds like a big, artificial fix, which from my experience doesn't often work and often leads to more unplanned problems," says Paul Csagoly, an expert who worked on a project to clear fish that had been introduced to eat grass in the Danube River.

Some bad examples
History is replete with examples of the dangers of messing with Mother Nature.

Toxic cane toads imported for beetle eradication on sugar cane plantations are a threat to Australia's indigenous wildlife. Mongooses introduced to the Hawaiian islands in the 19th century ended up doing more harm to native birds than to the rats they were meant to kill.

Still, the folks in Chaohu seem to figure they have little to lose.

A decade ago, the lake was already rated dangerously polluted. Loans from the Asian Development Bank helped pay for upgrading some heavily polluting factories and building sewage treatment plants.

All to little avail. Two industrial cities of 5 million — Chaohu to the northeast and Hefei to the northwest — flank the lake, providing a steady diet of nitrogen, phosphorous and other nutrients to algae that last summer turned wide swaths of the lake a brilliant algae green, and then putrid black.

"Economic development has had a negative impact on the lake. We're just finding ways to counteract that," Che says.

The cleanup involves more than just stocking the lake with carp fry, says Ding Zhisong, deputy director of Chaohu's environmental bureau. He shows off a grove of trees planted in contaminated silt dredged from the lake.

AFP-Getty Images A fisherman looks out from his boat April 18 on Taihu Lake, China's third-largest, where a pollution-linked algae bloom reappeared.

Dozens of fishing boats are moored nearby, their occupants busy mending nets and painting, since the lake is closed to fishing until mid-June.

The water's edge is a soapy froth mixed with trash; the only sign of aquatic life, a tiny freshwater shrimp meandering through thick green fronds of algae.

Most environmental experts warn against consuming carp and other bottom feeders from lakes such as Chaohu that are contaminated not just with algae but also with toxins such as lead, cadmium, mercury and arsenic.

Though the official government line is that the fish are fine, Yvonne Sadovy, a Hong Kong University professor who sometimes meets with fisheries experts in China, said some of them have expressed concern.

While silver carp sometimes can consume toxic algae without becoming poisonous themselves, they also may absorb other contaminants, says Celia Chen, a Dartmouth College professor who has researched how pollution affects the food chain.

"I would ask myself as a scientist and as a consumer, 'What would make me comfortable eating the fish?' and that would be knowing the fish tissue did not have contaminants in it," she said in an e-mailed response to an inquiry.

She noted that most fish in China are never tested because of the expense involved.

"I wouldn't eat them on a regular basis," she said.

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