Mystery Solved

The most contaminated reservoir in El Salvador is also hugely popular with migratory birds. So much so that scientists are extremely concerned - about the birds. The pollution itself, not so much - or they'd clean it up instead of wondering about why the birds find it attractive. 

Built in 1974 to drive El Salvador's biggest hydroelectric project, the 33,360-acre (13,500- hectare) Cerron Grande reservoir collects some 3,800 metric tons of excrement each year from the sewage pipes, as well as factory run-off and traces of heavy metals like chromium and lead, the government estimates.

So scientists are puzzling over the fact that some 150,000 seabirds from more than 130 species have chosen to make the reservoir their home. At least 90 of the species are migratory birds arriving from as far away as Alaska.

"It's one of the most contaminated lakes we have, which is why we should carry out a study on why the birds are here," said marine biologist Oscar Molina.

Waste from 54 industrial plants, 55 coffee processing plants, seven sugar mills and 29 sewerage systems flows into the reservoir, the environment ministry found in a 2004 study.

Yet the birds attracted to the lake even outnumber the roughly 100,000 people living in villages around it.

On one of 28 islands dotting the reservoir, biologists discovered 46 nests made by migrating American storks who produced some 100 chicks at the start of the year.

The scientists are, as usual, overlooking the obvious. The outflow from 55 coffee processing plants and seven sugar mills is in the water. So storks are obviously coffee fiends! If they added the output from some dairy processors, they also capture the swan market, swans being notoriously hooked on lattes.