As sea levels rise in the Bay, cities are scrambling to figure out how to prepare. Some cities are contemplating multi-benefit, nature-based solutions and managed retreat for critical infrastructure. Unfortunately, San Mateo County is going it alone—and they’ve just put forward a terrible idea.

An inter-governmental agency known as OneShoreline has proposed armoring the San Mateo County shore with sea walls, starting with a 2.65-mile wall in the Bay between Burlingame and Coyote Point.

But sea walls are generally a bad idea in a place like the Bay, which is shaped like a giant bathtub.

When waves ricochet off hard surfaces, their force intensifies against un-armored areas nearby. So hard barriers can make flooding stronger and increase sea level rise in neighboring communities. Analysis shows that a wall along San Mateo could have a negative impact as far north as San Pablo Bay.

Walls also inhibit healthy water circulation, creating breeding grounds for harmful algae blooms, and alter the surrounding water’s chemistry. This wall would require a network of pumps and other equipment to prevent the Bay’s shoreline from turning into a series of fetid moats.

That’s why we partnered with a coalition of experts to challenge the OneShoreline project for what it is: one area armoring itself at the expense (literally) of its neighbors and the entire Bay ecosystem.

The proposal is particularly egregious given that San Mateo is the wealthiest county in the Bay Area. The wall’s effects would be felt in areas throughout the Bay, including communities with few resources to adapt to even greater sea level rise and flooding.

The good news is that there are sound, regionwide plans for sea level rise, such as the Adaptation Atlas from the San Francisco Estuary Institute and an upcoming plan from the Bay Conservation & Development Commission.

Why would one county build a wall that would exacerbate sea level rise and algae outbreaks for the rest of the Bay Area? We all share the Bay, and by working together on a regionwide plan, we can make the entire shore resilient to sea level rise and flooding.

Pictured: A map of the first leg of San Mateo’s planned sea wall (in purple) in the Bay, which Baykeeper and local community groups are opposing.