Minus Tides: What a Negative Tide Means and When They Happen

A minus tide, also called a negative tide, is a low tide that drops below 0.0 feet on the tide chart, lower than the average daily low. On the Marin coast these tides come in runs of a few days around the new and full moon, and they uncover reef, sand and sea life that stay under water most of the month.

They are the tides tidepoolers wait for. A -1.5 foot low at Duxbury Reef or Sculptured Beach opens up rock you will not see on an ordinary day.

What Does a Minus Tide Mean?

Every height on a tide chart is measured from a zero line called mean lower low water, or MLLW. NOAA sets it as the average height of the lower of the two daily low tides over a 19-year period.

A minus tide is any low that falls below that line. A -0.5 foot tide is half a foot below the average daily low. A -2.0 foot tide is two feet below it, close to as low as the Marin coast gets. The minus sign does not mean the water is gone, only that it is lower than usual.

For more on reading the numbers, see how to read a tide chart.

Next Daylight Minus Tides

Low tides below zero between sunrise and sunset in the next 90 days.

Why Minus Tides Happen

Minus tides are spring tides. Around each new and full moon, the sun and moon line up and their pulls add together, so the highs run higher and the lows run lower. The lowest of those lows dip below zero.

They are deepest when a new or full moon falls near perigee, the moon’s closest point to Earth. Those same days give the highest high tides of the year in winter, so the deepest winter minus tides and the king tides often fall on the same days. The spring and neap tides guide explains the cycle.

When Minus Tides Happen in Marin

Minus tides come most months on the Marin coast. NOAA’s 2026 predictions for Point Reyes show at least a few in every month, with the most in May and June and the fewest in August and September.

The time of day follows the season:

Season	When the minus tides fall
Late spring and summer	Before dawn to mid-morning
Late summer and early fall	Mostly at night, with few in daylight
Late fall and winter	Afternoon and evening, often near sunset in November and December
Early spring	Shifting from afternoon toward morning

That pattern decides when you can use them. A deep minus tide at 3 a.m. in July is no help on a reef. The useful ones are the early mornings of May and June and the afternoons of January and February. The deepest predicted lows of 2026 at Point Reyes, a little over 2 feet below zero, came in May and June.

The tide arrives later inside the bays. On average, NOAA predicts low tide at Inverness about an hour and a half after Point Reyes, so check the station for your spot, such as Point Reyes or Duxbury Reef.

Why Tidepoolers Care About Minus Tides

Many tidepool animals live low on the shore, where they stay wet most of the time. Only the lowest tides expose that zone. The National Park Service says the best time to go tidepooling is during a minus low tide, and that not every low tide drops far enough.

Plan to arrive at least an hour before the low and leave no later than an hour after the water starts rising. The best Marin spots for this are Duxbury Reef at Agate Beach and Sculptured Beach south of Limantour Beach. The tide pools guide covers each one, along with the rules on Duxbury Reef, where taking any shell, rock or animal is illegal.

Staying Safe During a Minus Tide

A minus tide pulls you farther out than usual, onto rock that the ocean covers most of the time. That is where sneaker waves are most dangerous. The National Park Service says tidepoolers have died at Point Reyes beaches after being struck by them. Never turn your back on the ocean.

Keep track of the time. The water rises again soon after the low, and at Sculptured Beach and McClures Beach the incoming tide can cut off the way back. The Park Service warns that at high tide on Sculptured Beach there is no way out.

On Tomales Bay a minus tide brings a different problem. Low water exposes wide mudflats at the south end of the bay, and the Park Service warns that kayakers can get stuck at Millerton Point and White House Pool. Plan a launch there around a higher tide.