USAToday reports that one of the more controversial proposals in the food safety debate would require that farmers plow under a buffer zone between fields and "undisturbed, open, non-farmed land with evidence of wildlife," as well as ponds, rivers, wetlands and creeks. But many point out that the overwhelming evidence is that cattle manure, not wild animals, is the primary source of E. coli O157:H7. A study out this month in The Journal of Food Protection found that 3.6% of beef cattle and 3.4% of dairy cattle carry the dangerous strain.

The most recent drafts of the proposal would require that buffer to be anywhere from 30 feet to a quarter-mile wide, says Linda Sheehan, executive director of the California Coastkeeper Alliance.

"There’s no scientific support for believing that ripping out any plants alongside rivers is going to help," Sheehan says. In fact, there is strong evidence that vegetation around waterways creates a living filter that captures some of the pathogens present in animal waste, keeping them from the water that might eventually be used to water crops, she says.

Requiring farmers to plow under vegetation up to waterways could also severely degrade water quality, because plants help protect stream banks against erosion, said Daniel Mountjoy of the Natural Resources Conservation Service of the state Department of Agriculture.