If rivers are a nation鈥檚 lifeblood, the US should be on the sick list. More than half of the country鈥檚 streams and rivers are in a 鈥減oor condition鈥� for aquatic life, according to .
The agency sampled nearly 2000 sites in 2008 and 2009, looking at factors such as physical disturbances, mercury in fish flesh, faecal bacteria and nutrients from fertilisers.
Nutrient pollution, which causes algal blooms that can deplete a river鈥檚 oxygen, was the main problem: 40 per cent of rivers and streams were rated 鈥減oor鈥� for their high levels of phosphorus and 28 per cent were given the same rating for excessive nitrate contamination. Nitrates are the more persistent contaminant as they leach into groundwater and from there into streams. A new study suggests nitrates will cause pollution for decades to come, even without further fertiliser use.
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Phosphorus pollution is also a growing problem. Only 34.2 per cent of river stretches tested were rated in 鈥済ood鈥� condition for phosphorus, .
Unfortunately, not all farmers observe official guidance on fertiliser use. 鈥淚f everyone followed it, things would probably be quite a bit better,鈥� says Neil Dubrovsky, a US Geological Survey hydrologist based in Sacramento, California.
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This article will appear in print under the headline 鈥淐ry me a river鈥�
