Over half of America's homeowners regularly douse their yards with pesticides, some of which, recent research indicates, may cause reproductive harm to wildlife and people. This March, the U.S. Geological Survey announced that pesticides were found in almost all waterways and in some drinking-water systems. The January 2006 Food and Chemical Toxicology showed that 2,4-D, a widely used residential herbicide, reduced weight gains in rat pups. In June 2005, Science reported that high concentrations of the lawn- and garden-spray ingredients methoxychlor and vinclozolin caused hereditary changes in mice, affecting male fertility. Other pesticides contain organophosphates--chemicals that attack the nervous system and are linked to hermaphroditism in amphibians as well as low birth weight in humans, fish, lizards and plants, according to the EPA.

Although synthetic pyrethroids are touted by manufacturers as less toxic, two 2005 studies found that the varieties lambda-cyhalothrin and bifenthrin, both used on residential lawns and gardens, proved lethal to fish at concentrations of only 2 to 6 parts per billion (ppb). In California streams, levels were measured as high as 437 ppb.

Fertilizers pose their own problems. "All plants need nitrogen, phosphate and potassium, but many synthetic fertilizers deliver them in a fast-release, water-soluble form they can't take up all at once," says Karl Guillard, Ph.D., professor of agronomy at the University of Connecticut. These nutrients seep into waterways and contribute to algae bloom.