It’s well-known that the dark side of suburbia’s love affair with green lawns has been polluted runoff that wreaks havoc with marine life in bodies of water such as the Chesapeake Bay.

But in the wake of a new Virginia law that will ban some uses of phosphorous-based lawn fertilizers, several conservation groups and a major lawn fertilizer company have teamed up for a wide-ranging forum on protecting water quality in Fairfax County, home to more than 1 million suburbanites.

The Virginia Conservation Network, which includes more than 100 organizations, and Scotts Miracle-Gro Co., which produces many lawn and garden products for consumers, will be hosting a public forum at George Mason University on Thursday to discuss urban stormwater runoff, green infrastructure and various ways that homeowners can help protect the Chesapeake watershed.

The forum will range from the big picture to the minute, as a panel discusses the overall efforts to protect the Chesapeake Bay, and new landscaping procedures and lawn-and-garden practices that can contribute to clean water, said Nathan Lott, executive director of the Virginia Conservation Network. He said organizers hope to attract urban planners, community leaders, representatives of homeowners associations and members of other advocacy groups from Northern Virginia.

“If can just change the practices of 25 percent of the million people in Fairfax County, imagine what kind of impact that would have,” Lott said. “That’s why we picked the GMU area.”

Lisa Guthrie, executive director of the Virginia League of Conservation Voters, said the alliance between conservation groups and the fertilizer industry comes as a new law takes effect that will eventually restrict the use of phosphorous. The new law, sponsored by Sen. Richard Stuart (R-Westmoreland), will ban the use of phosphorous fertilizers to maintain people’s lawns by 2014, but will still permit the use of such phosphorous-based fertilizers on new lawns and other applications.

The measure also restricts snow removal and de-icing compounds that contain nutrients such as phosphorous and creates new reporting regulations for lawn-care firms that spread fertilizers on nonagricultural properties of more than 100 acres. It requires golf courses to begin implementing plans for managing fertilizers and runoff by July 1, 2017.

The law, which passed the General Assembly this year with large margins of support, represents a compromise hammered out between the lawn care industry and conservation groups, Guthrie said.

“We did support it,” Guthrie said. “It’s not an aggressive restriction on fertilizers. ... [But] it’s probably a good thing, especially in suburban areas.” The new law became effective July 1, but its ban on using phosphorous fertilizers for lawn maintenance will not begin until Dec. 31, 2013.

Plant nutrients such as phosphorous and nitrogen, which enter the watershed from agricultural runoff, fertilized lawns and other activities, can trigger explosive algae growths that eventually deplete the water’s oxygen supply, creating “dead zones” in parts of the bay.

The forum, titled Urban Water Quality: Community-Based Solutions,” will be held at George Mason University’s Mason Hall on Thursday July 21 from 9 a.m to 12 p.m. The panel of speakers includes Lott; Chris Wible, director of environmental stewardship at Scotts Miracle-Gro Co.; Mike Goately, a professor at Virginia Tech who specializes in turfgrass with the university’s extension; Randy Bartlett, director of Wasterwater and Stormwater; Asad Rouhi of the Northern Virginia Soil and Water Conservation District; Dann Sklarew of the GMU Potomac Environmental Research and Education Center; and Lenna Storm of the GMU Sustainability Institute.

Although the forum is open to the public, organizers ask that people who are interested in attending also RSVP so that appropriate accommodations can be made. To register, go here on the Virginia Conservation Network’s Web site.