Efforts to restore watershed habitats throughout California, including several in the Bay Area, are threatened because the state is using a largely unknown law to force nonprofit groups to pay prevailing wages to volunteers on their publicly funded projects. "This serves as a de facto prohibition on volunteerism as perhaps every community project in these dire fiscal times uses some level of volunteer assistance,'' Michael Wellborn, president of the California Watershed Network, wrote in a recent letter to Gov. Arnold Schwarzenegger. The issue came to a boil after the state Department of Industrial Relations, responding to a labor union's complaint,...