The problem isn't fertilizer per se, but what critics say has amounted to an overenthusiastic use of it.
Residents may think they're merely fertilizing their lawns, but in reality they're also growing a bumper crop of algae in the nearest body of water.
Every time it rains, the excess nutrients are flushed into streams, lakes, and bays. The algae, in addition to sliming swimmers and looking gross, consume oxygen that is vital to aquatic organisms.
The debate has played out in a half-dozen states from New York to Florida, transforming the once-fallow field of fertilizer law.
Traditionally, laws were aimed at things such as truth in labeling. Now, "it's evolving from consumer protection to environmental protection," said Chris J. Wible, director of environmental stewardship for The Scotts Miracle-Gro Co., a major fertilizer manufacturer, based in Marysville, Ohio.
Pennsylvania has taken no formal action on lawn fertilizers, but some products are changing anyway.
As part of an agreement with advocates for Chesapeake Bay - which drains about half of Pennsylvania - Scotts has voluntarily reduced the phosphorus in the lawn fertilizers it distributes to states in the bay's watershed.
Action on nutrient pollution in Pennsylvania has focused on sewage treatment plants, which are facing tighter discharge restrictions, and agriculture, which has made consistent strides in reduced - and more effective - use of manure and fertilizer.
In most states, discussions about lawn fertilizer "are really in their infancy," said scientist Harry Campbell of the Pennsylvania office of the Chesapeake Bay Foundation. But there is a growing recognition that homeowners and fertilizer are often a recipe for excess, he said.
The problem is "the political palatability of the solutions," Campbell said.
In New Jersey, for example, phosphorus would be pretty much out of the mix, except for new lawns. Nitrogen would also be limited.
Residents would be prohibited from applying fertilizer before a heavy rain. Or between Nov. 15 and March 1. Or within 25 feet of a water body. Or on impervious surfaces. No more letting stray granules spritz onto a nearby driveway or sidewalk.
Among critics of the New Jersey bills are the fertilizer and turf industries. They say that they support the concept, but call the curbs too strict.
Retailers have also complained. Are they supposed to be the phosphorus police?
Critics warn further of a reverse effect: More fertilizer use. If the new products are inferior, residents who do not get the desired results may just apply another dose.
In New Jersey, the poster waterway for the issue - and the main focus of the bills - is Barnegat Bay.
A signature coastal estuary that stretches from Point Pleasant Canal to Little Egg Harbor inlet, its shores are lined with homes and docks.
Its value to the local economy is estimated to be more than $3 billion annually.
The fertilizer problem is exacerbated in the Barnegat watershed because of the sandy soil. Lush lawns require frequent jolts of fertilizer, but they quickly wash away.
In the bay's shallow waters, flotillas of nitrogen-fueled algae shade and kill the sea grass beds that drive the bay's ecosystem and support its fish, crabs, and clams - all of which have declined.
The water chemistry is changing, making the bay more hospitable for stinging jellyfish called sea nettles.
In August, a "brown tide" algae bloom that is toxic to scallops hit the lower bay.
Before, the problems were evident only to scientists. Now, "it's becoming visible to the average person," said Rutgers University marine scientist Michael J. Kennish.
"This is an environmental jewel that is rapidly tanking," said Sen. Bob Smith (D., Middlesex), one of the sponsors of the fertilizer bill.
Smith and Assemblyman John F. McKeon (D., Essex) - both chairmen of legislative environmental committees - introduced fertilizer bills as part of a suite of measures to heal Barnegat Bay.
One is aimed at failed storm-water basins that allow nutrient-laced runoff to gush through. Another addresses construction practices that compact the soil, making it less able to absorb rain.
Others are specific to Ocean County, which surrounds Barnegat Bay. One would allow the county to collect a storm-water tax. The freeholders have opposed it.
But it is the fertilizer bills that have generated the most debate.
A sticking point is uncertainty over the source of the 1.4 million pounds of nitrogen that enter the bay every year.
For a county with virtually no industrial pollution, agriculture, or sewage discharge - pipes carry it a mile out into the ocean - where is all the nitrogen coming from?
The general pathways are known. A U.S. Geological Survey study found that 66 percent of the nitrogen comes from land and 12 percent from groundwater.
An additional 22 percent literally falls from the sky. Produced by fossil-fuel combustion - in cars and coal-fired power plants, for instance - it is transported by wind.
But as for more specific sources, the science is less clear. One modeling study suggests fertilizer contributes 17 percent. The fertilizer industry says sales figures and other data point to a figure of 2 percent.
Robert Nicholson, a Geological Survey hydrologist, said scientists were hoping to use isotope analysis to fingerprint the nitrogen sources.
Research has shown that restrictions help. In one study, a University of Michigan ecologist found that nutrient levels - in this case, phosphorus - in the Huron River dropped 28 percent after Ann Arbor adopted an ordinance that limited its use on lawns.
Meanwhile, in New Jersey, debate continues. Nancy Sadlon, executive director of the New Jersey Green Industry Council, which represents fertilizer-makers and lawn-care companies, said the cutoff date of Nov. 15 is four weeks before what most industry standards suggest.
With a shorter season, she said, some lawn-care companies might go out of business.
Scott's Wible said he had issues with the amount of slow-release nitrogen the bills would require.
Less soluble, it would be less likely to be carried away by rain. But he said the 30 percent requirement is arbitrary and would make it difficult for a homeowner to maintain a healthy lawn.
Compared with a balding lawn, healthy turf "knits the soil together" so it can absorb more rainwater, he said. "We really need it in urban environments."
Still, water advocates and environmental groups - such as the Sierra Club, Environment New Jersey, the American Littoral Society, and Clean Ocean Action - have lined up solidly behind the fertilizer restrictions.
Jane Nogaki of the nonprofit group Clean Water Action said the measure could also lead to a reduction in the use of other chemicals, particularly herbicides that lake managers often use to kill algae.
Advocates want fertilizer sold to have 30 percent slow-release nitrogen so it cannot wash away all at once. "The analogy would be that if someone's going to misbehave," said William DeCamp Jr., head of the nonprofit Save Barnegat Bay, "let them do it with a BB gun, not a bazooka."
Contact staff writer Sandy Bauers at 215-854-5147 or firstname.lastname@example.org Visit her blog at http://go.philly.com/greenspace