Tomales Bay Bioluminescence: When and How to See the Glow

Tomales Bay bioluminescence is a blue-green glow made by tiny plankton called dinoflagellates, and it shows up best on dark summer and fall nights when the moon is down. Every paddle stroke, splash or passing fish sets off a flash of light in the water.

The National Park Service calls Tomales Bay one of the most popular places on the Point Reyes coast to see it, though the glow can turn up anywhere along the National Seashore. Most people see it from a kayak on a guided night paddle.

What Causes Bioluminescence in Tomales Bay?

The light comes from dinoflagellates, single-celled plankton that have traits of both plants and animals. The kind in Tomales Bay is often called “sea sparkle.” When the water around them is disturbed, a chemical reaction inside each cell gives off a short burst of light.

That is why the glow follows movement. A still bay looks dark. Drag a paddle through it and the water lights up along the blade, and drips falling off the paddle flash as they hit the surface. Bioluminescence makes little or no heat.

Scientists think the flash may help these cells startle or expose the animals that eat them. Ocean researcher Edith Widder has called it a “bioluminescent burglar alarm,” as the Park Service explains.

Next New Moons Over Tomales Bay

The darkest nights fall around each new moon. Dates and sunset times for Tomales Bay:

• Sunday, November 8, 2026sunset 5:05 PM
• Tuesday, December 8, 2026sunset 4:51 PM
• Thursday, January 7, 2027sunset 5:06 PM
• Saturday, February 6, 2027sunset 5:39 PM
• Monday, March 8, 2027sunset 6:11 PM
• Tuesday, April 6, 2027sunset 7:38 PM

Tonight the moon is waning gibbous, 60% lit.

Best Conditions for Seeing the Glow

Darkness matters more than anything else. The Park Service says the best viewing is in summer and fall, on dark, cloudy nights before the moon has risen or after it sets. A bright moon washes the glow out, which is why night tours on the bay are scheduled near the new moon.

Condition	Why it matters
Summer and fall	The season the Park Service names for the best viewing
New moon, or moon below the horizon	Moonlight washes out the faint flashes
Cloud cover	Blocks starlight and any moonlight
Calm water	Each stroke shows up clearly instead of mixing with chop
Away from town lights	Lights on shore cut the contrast

Keep your own lights dim, too. The Park Service suggests red LED or red-filtered lights, since white light ruins your night vision. It can take several minutes in the dark before your eyes catch the faint flashes.

The glow is not the same every night. Plankton numbers change from week to week and from year to year, so one dark night can be bright and the next nearly blank.

How People See It: Night Kayaking

The usual way to see Tomales Bay bioluminescence is a guided night kayak tour that launches from the bay shore after dark. Guides bring boats, lights and life jackets, and they know which stretch of water to use given that night’s wind and tide.

If you paddle at night on your own, follow the Park Service boating safety rules. It strongly recommends a working 360-degree light on every kayak and canoe so other boats can see you. Personal flotation devices should be worn the whole time.

Mind the launch rules as well. Tomales Bay State Park, which includes Heart’s Desire Beach and Millerton Point, is open from 8 a.m. to sunset, and overnight parking is not allowed. Plan your launch at a site that allows evening use, and check the rules before you go. The Tomales Bay kayaking guide covers each launch site.

How the Tide Matters on a Night Paddle

The tide decides where you can paddle and how hard the trip home will be. The change between high and low tide drives strong currents, especially near the mouth of Tomales Bay. A paddle out on the ebb can turn into a slog back against the flood, and that is harder to judge in the dark.

Low water also exposes mudflats at the south end of the bay. The Park Service warns that you can get stuck at Millerton Point or White House Pool at low tide, and Millerton Point is very shallow and best used at high tide. Getting stuck on a mudflat at night is cold and slow to fix.

Tide timing inside the bay runs later than on the coast. NOAA predictions put the tide at Inverness roughly an hour and a half behind Point Reyes on average. Check Tomales Bay tides or Inverness tides for the spot where you plan to launch.

Safety on Tomales Bay at Night

Cold water is the biggest danger. The Park Service warns that cold water drains body heat much faster than cold air, and that shivering, slurred speech and stumbling are signs of hypothermia. Dress for a swim, not for the air.

Wind is the other risk. Tomales Bay can act as a wind tunnel as northwest winds funnel between Inverness Ridge and Bolinas Ridge, and the afternoon wind is usually stronger than the morning wind. If it is still blowing hard at dusk, the water will be choppy and the glow harder to see anyway.

Stay at least 300 feet from harbor seals, which haul out along the bay. The east side of Hog Island is closed to the public all year. Keep your group close together, and make sure someone on shore knows when you plan to be back.