What Will Happen to Bair Island with Sea Level Rise?

Every winter during the King Tides, I make a point of visiting POST-protected Bair Island to witness a worrying harbinger of the future. It might sound like a grim ritual, but as someone who cares deeply about California’s shorelines, I find it both sobering and fascinating. King Tides happen only twice a year when the sun, moon, and Earth align, creating unusually high water levels. These conditions offer a kind of natural sneak peek at what everyday tides could look like as sea levels continue to rise. (Interested in seeing the King Tides for yourself? Mark your calendar for December 4-5, 2025 and January 2-3, 2026!)

The experience is always striking. Standing on a sidewalk just east of downtown Redwood City, I watch seawater as it seeps through cracks in a retaining wall, spills into the gutter, and trickles down the street. The spot where I stand — normally high and dry — becomes briefly washed over with frigid winter saltwater. It’s a vivid reminder of how today’s extremes could become tomorrow’s daily norms.

In the video below, you can get a glimpse of what these rising tides look like from the side of a boat (along with some camera-ready shorebirds and other wildlife):

An experience like this one has a way of surfacing some big inquiries. What will the San Francisco Bay look like in the future? What will happen to places like Bair Island, one of the largest islands in the bay, as the sea rises? And what are we doing to prepare for this new reality?

These are complicated questions and  an array of experts are researching and implementing plans to get ready and intervene. There’s still plenty to discover, but we’ve already learned a lot about sea level rise and how it will affect the future of the San Francisco Peninsula and its natural lands.

Sea level is rising faster than we expected.

Since the turn of the 20th century, the oceans have risen more than eight inches. Scientists expect this trend to accelerate in the coming decades and that, by 2050, our oceans might rise around one foot!

We need the Bay’s baylands more than ever.

The baylands of the San Francisco Bay, the marshy habitat found at the water’s edge, play an important role in buffering our communities from storm surge and provide habitat for many critically endangered species of wildlife. As sea level rise accelerates, we will rely on this landscape more and more to protect our communities from coastal flooding and provide refuge for local plants and animals.

Sea level rise is threatening the bayland ecosystem.

The wildlife of the baylands have adapted to intermittent flooding like the King Tides I witnessed, but to survive and be healthy, their habitats need time to dry out—something that might become impossible as the sea level continues to rise. Wetlands drowned by the rising sea would eventually be transformed into large mudflats. Devoid of vegetation, they would no longer support the wildlife they do today or be as effective at buffering our communities against storms.

But the baylands themselves are rising too (and that’s good news)!

With each passing tide, large quantities of sediment from our local creeks and rivers redistribute throughout the bay. As currents slow, these sediments settle and accumulate within our bayland marshes, causing the bayland soils to creep higher over time.

You can see this best at Bair Island. Many decades ago, settlers leveed the island—that is, built an embankment to prevent the flow of tidal waters—and used the landscape for ranching cattle, farming, and salt production for much of the last century. In 1997, POST protected 1,623 acres of Bair Island and it is now protected as part of Don Edwards San Francisco Bay National Wildlife Refuge managed by U.S. Fish and Wildlife Service.

With our partners’ help, we worked to restore the land back to its natural state by removing the levees. The final levee was breached in December of 2015, allowing the rich waters of the bay to return and nourish the island landscape ever since. Sediment from the bay is now being deposited here and the island is once again on the rise. See it for yourself:

Sediment planning is underway.

The truth is that there’s still a lot of debate about exactly how extensive the impacts of climate change will be here in our corner of California. And to know exactly what the future will hold for places like Bair Island, we first need to have a better understanding of the changes that are coming to the region as a whole.

One thing that is certain is that the San Francisco Bay needs more sediment to buffer against sea level rise. But just how much sediment will we need and where will it come from? In 2021, our partners at the San Francisco Bay Estuary Institute (SFEI) released the results of an illuminating analysis. 

This report looks at current data and future climate predictions to outline a plan to strengthen shoreline habitats and support healthier watersheds. Here are some important takeaways.

• Tidal marshes and mudflats are unlikely to receive enough sediment naturally to survive sea-level rise during this century.
• Restoring thousands of acres of historic marshes to the tides is invaluable to protect the shoreline, maintain the health of the Bay, and ensure that tidal marshes and flats will be resilient as the climate continues to change.
• Between now and the year 2100, the amount of sediment that gets stuck in watersheds, removed from the Bay, or dug up during construction projects will probably be greater than the amount of sediment flowing into the Bay from local rivers and the Delta.
• We need to update how we manage sediment — and fast — so we can tap into other sources that help tidal marshes and mudflats survive in the future. Doing this will take quick, coordinated teamwork among public agencies, industry, and many others, along with new, creative approaches to how sediment is handled and regulated. 

You can see the King Tides for yourself.

Seeing the King Tide events opened my eyes to the complexity of this place and the challenges we face as stewards of this landscape. The questions I started with have only led me to more questions. To jumpstart your curiosity about our region’s future, get out there and see Bair Island for yourself  (and, if you want to align your visit with the King Tides, be sure and consult the tides map).