In May 1998, more than 170 people got sick after eating raw oysters from Tomales Bay. Although the source of the problem was never pinpointed, the Norwalk-like virus that sickened people could only have come from human waste.
State health officials believe the outbreak was caused by a boater who dumped waste overboard, a camper who improperly handled waste, or a leaking septic system.
Since then, efforts have been made to educate fishermen and others about the problem and more portable toilets have been placed around the shoreline.
Phil Smith, environmental health services director for Marin County, said his agency has advised homeowners on how to maintain septic systems.
In addition, the county plans to build a new treatment system for at least 20 homes along Tomales Bay with $1 million in state and federal grants.
Smith also plans to continue the popular "septic socials" to help homeowners better understand their septic systems. People competed for reservations to attend one of the earlier events.