Elizabeth Campbell, who in January proposed a citizen initiative to fight a waterfront highway tunnel, will declare this afternoon she's running for mayor.

Campbell, 56, is a neighborhood advocate in Magnolia who opposed housing development inside Discovery Park. She is studying for a master's degree in public administration at the University of Washington. Earlier in her career, Campbell arranged development deals for health-care facilities, and started a commercial-baking company.

Her anti-tunnel Initiative 99 is off to a slow start. Campbell said she has 3,500 signatures to date, of the 18,000 needed to qualify by early August.

Gov. Chris Gregoire, Mayor Greg Nickels, and former King County Executive Ron Sims announced early this year that they've agreed a tunnel will replace the Alaskan Way Viaduct. The tunnel beneath First Avenue, along with an elevated Sodo interchange, totals $3.1 billion, and another billion or so would go for related seawall, parks, transit and road improvements.

Campbell describes herself as populist. In a press release, she says the Nickels administration has "very deliberately and methodically been dismantling neighborhoods, displacing whole classes of people."

Her campaign announcement is 3 p.m. today at Smith Cove Park, along the north shore of Elliott Bay. Campbell becomes the seventh candidate in the race.