If you walk the levee along Beach Park Boulevard, have you ever passed the Shellbar at low tide, seen mostly mud and shells, and kept going? Come back on a high-tide morning between September and April and the same spit can hold thousands of resting shorebirds. Sequoia Audubon Society's county birding guide calls it one of the best places in San Mateo County, and even in all of Northern California, to watch shorebirds. In November and December, this winter's highest tides peak between mid-morning and just after noon, and two of those days are Thanksgiving and Christmas.
A Shell Spit a Mile South of the Bridge
The Shellbar is a large spit about a mile south of the San Mateo Bridge. It sticks out into the Bay from Beach Park Boulevard and is built from clam, oyster and mussel shells, which is how it got its local name. The way you reach it changed with the City's levee rebuild. Foster City's Levee Improvements Project is finished. The full Bay Trail reopened in October 2023, and the contractor reached final completion in February 2024. The City held the ribbon cutting at Shorebird Park on February 21, 2024. The rebuilt trail is 18 feet wide, with 12 feet of asphalt and decomposed-granite shoulders, and it has separate marked lanes for cyclists and pedestrians.
Sequoia Audubon's guide was updated for the new levee and lists three places to stand along this stretch:
- Beach Park Boulevard at Tarpon Street, across from Bowditch Middle School. This is the main access point, with a large viewing area and stairs down to the spit.
- Between Tarpon and Marlin, a smaller stairway.
- Across from Marlin, a large viewing area with no stairs. The guide calls it the best spot for seeing huge numbers of shorebirds on the riprap at high tide.
You don't have to go down onto the shells at all. According to the guide, the levee wall is low enough that you can see the whole Shellbar from the walkway. It also warns that the spit has no real trails, the raised shellbeds aren't always stable, and visitors should stay far enough away that the birds aren't disturbed.
Why the Clock on the Tide Matters More Than the Calendar
Shorebirds feed on open mudflats while the tide is out. As the water rises it covers their feeding grounds and pushes them onto the few high, dry places left. On this part of the shoreline, the Shellbar is one of those places. Sequoia Audubon says the best viewing is just before and just after the peak of high tide, from September through April.
So two walks on the same path a few hours apart can look nothing alike. At a midday low tide you see shells. At a late-morning high tide you see the flocks the guide describes. The guide also says mornings are best for birding Foster City generally, and that October through March is when water birds winter here by the thousands. The ideal visit is a winter morning when high tide also falls in the morning, and that doesn't happen every week.
Seven High Tides Between 9:44 a.m. and 12:26 p.m.
The California Coastal Commission's King Tides Project lists this winter's statewide King Tide dates as November 24 to 26, 2026, December 23 to 25, 2026, and January 21 to 22, 2027. It adds that Northern California may also see them on December 22, January 20 and January 23. King Tides are the highest tides of the year.
For local timing, NOAA's tide predictions for its Bay Slough, west end station put the November and December peaks between mid-morning and just after noon:
| Date | Day | Predicted high tide | Height (ft, MLLW) |
|---|---|---|---|
| November 24 | Tuesday | 10:53 a.m. | 9.37 |
| November 25 | Wednesday | 11:37 a.m. | 9.49 |
| November 26 | Thursday, Thanksgiving | 12:26 p.m. | 9.38 |
| December 22 | Tuesday | 9:44 a.m. | 9.46 |
| December 23 | Wednesday | 10:34 a.m. | 9.71 |
| December 24 | Thursday, Christmas Eve | 11:25 a.m. | 9.76 |
| December 25 | Friday, Christmas Day | 12:18 p.m. | 9.55 |
Ordinary weeks look different. On Sunday, December 6, NOAA predicts a 9:47 a.m. high of 8.49 feet. On Saturday, December 12, the day's high comes at 1:16 p.m. and reaches 7.55 feet. On Christmas Eve the high is about two feet above that mid-December Saturday, and it arrives before lunch. NOAA tracks the station against San Francisco's reference station and adjusts the times and heights for local conditions. These are predictions, so check NOAA's tide page for the station the morning you go.
The holiday dates are worth noting if you're hosting. A walk timed to the 12:26 p.m. high on Thanksgiving fits before an afternoon meal. On Christmas Day the peak is at 12:18 p.m.
What the Flocks Look Like in Winter
Sequoia Audubon says the Shellbar is the best place in the county to see Red Knots and Black Skimmers, and that the skimmers often show up in large numbers. In winter the Red Knots are in what the guide calls basic plumage, "without a trace of red," so a plain gray, stocky shorebird in the flock could easily be one. The guide also says Red Knots winter in Foster City in fairly large numbers.
The guide lists these birds using the spit as a resting place:
- Willets, both dowitchers, Marbled Godwits and Dunlin
- Western and Least Sandpipers
- Whimbrels and Long-billed Curlews
- Black-bellied and Semipalmated Plovers
- Black and Ruddy Turnstones, and Surfbirds on occasion
- Gulls and terns sharing the spit
The open Bay past the Shellbar fills up later in the season. Sequoia Audubon names November, December and January as some of the best months for Canvasbacks, American Wigeon, both scaup, all three scoters, Ruddy Ducks, goldeneyes, Buffleheads, loons and grebes. The guide also says to watch for Merlins and Northern Harriers looking over the shorebird flocks. When a whole flock lifts off the spit at once, a falcon is often the reason.
The guide recommends a spotting scope for birding Foster City. From the levee, binoculars will show you the flocks. A scope lets you tell a knot from a dowitcher.
Building a Morning Around One High Tide
Because the best viewing is just before and after the peak, you can plan a loop that puts you at the Shellbar at the right moment and then continues south along the water. One route based on the guide's directions:
- Arrive at Tarpon Street a little before the predicted peak. Start at the main viewing area across from Bowditch Middle School and scan the spit as the last of it disappears under water.
- Walk to the viewing area across from Marlin. The guide singles this out for big numbers of shorebirds on the riprap at high tide.
- Keep going toward Belmont Slough. The slough runs from the Bay near Halibut Street and Beach Park Boulevard toward the south end of Marina Lagoon, with a paved path beside it. The guide lists Great Blue Herons, Black-crowned Night-Herons, Great and Snowy Egrets, shorebirds and waterfowl there.
- Check the cement intake by Sea Cloud Park. You reach Sea Cloud Park from Edgewater Boulevard via Pitcairn Drive. At the intake there are benches with a good view of the slough, and the guide says Eurasian Wigeon often turn up there in winter.
For restrooms, the guide points to Bridgeview Park near the base of the bridge and Shorebird Park, where Beach Park Boulevard turns west. Both also have picnic tables. Sea Cloud Park has restrooms too. If your dog comes along, Foster City's park use rules say "No animals except on-leash dogs are allowed in the parks." Some of the guide's viewing spots are near homes, and it asks visitors to respect residents' privacy at all times.
Ducks have mostly moved off the lagoon at Leo J. Ryan Park. According to the guide, water birds on Central Lake dropped sharply after it was dredged in 2003, and most now turn up along Marina Lagoon, Belmont Slough, the Bay and the ponds at several condo and apartment complexes. That's the main reason a winter bird walk here heads to the shoreline.
When You Want Someone Else to Name the Birds
If you'd like to learn the gray winter shorebirds with a guide first, there are organized walks nearby. On Tuesday, November 24, the same morning as the first King Tide, the King Tides Project lists a 10:30 to 11:30 a.m. walk at the Ravenswood Unit in Menlo Park. San Mateo County Parks lists a two-mile "Who's That Bird?" walk focused on winter migrants at Coyote Point Marina and Shoreline on Saturday, December 12, from 9 to 11 a.m., and registration is required through County Parks. Coyote Point is only a short ride up the shoreline. Sequoia Audubon's guide says the bike path along East Third Avenue continues there from the Foster City shoreline. After that walk, the December 22 to 25 King Tides at the Shellbar make a good test of what you learned, and the January 21 to 22 dates give you one more try.
The Chirko Group keeps track of the dates that shape life along Foster City's shoreline, from levee walks to lagoon events. If you'd like to talk about the neighborhoods closest to the Bay Trail, request your no‑surprises consultation.
