It fights erosion, filters runoff, cools its surroundings, controls dust and makes for good picnics. A lawn can be nice to look at, but that can cause problems, depending on your aesthetic. The fertilizer can leach past the root zone and into streams and lakes, where it can cause algae blooms. Nearly half the people responding to a 1999 SPU survey said it's important their lawn be green. But the number of people feeling that way dropped 16 percent between surveys in 1994 and 1999.
Pesticides also can be a problem.
A 1999 study by the U.S. Geological Survey found nearly two dozen pesticides in King County streams, with concentrations of five pesticides exceeding federal limits set to protect aquatic life. They were detected in all 12 sample sites. Diazinon is believed to throw off a salmon's sense of smell, which it uses to detect predators. Oddly, many homeowners don't even know when they're applying pesticides to their lawns. Thirty-five percent said they had done so in the 1994 survey.