It depends on your coast. The internet's "−0.5 ft or lower" rule is a Southern California number: at La Jolla (NOAA station 9410230), daylight lows bottom out at −1.88 ft for all of 2026, so −0.5 ft is a genuinely good day. At Seattle (9447130), where July lows reach −3.8 ft, aim for −2.0 ft or lower. At Bar Harbor, Maine (8413320), ordinary lows near 0.0 ft already uncover plenty.
The −0.5 ft rule is folk wisdom, and like most folk wisdom it isn't wrong so much as unlabeled. It gets quoted in Washington and Maine as confidently as in San Diego. Here's what happens when you actually test it.
What does 0.0 ft measure in the first place?
US tide predictions are stated against a datum called MLLW, which NOAA defines as "the average of the lower low water height of each tidal day observed over the National Tidal Datum Epoch" — a 19-year averaging period, currently 1983 through 2001. In plain terms: take each day's lowest tide for 19 years, average them, call that 0.0 ft. At that station.
Those last three words are the trouble. The datum is computed per station, so 0.0 ft means "about average for a daily lowest low" everywhere. But how far below average a station ever gets varies enormously. A rule like "go at −0.5 ft" specifies a distance below a local average without saying whether that distance is remarkable. At some stations it is. At others it's Tuesday.
What does one threshold yield at three different stations?
We computed daylight low-tide windows for July 2026 at three stations with very different tides: Seattle inside Puget Sound, La Jolla at Scripps Pier, and Bar Harbor on the Maine coast.
| July 2026 | Seattle (9447130) | La Jolla (9410230) | Bar Harbor (8413320) |
|---|---|---|---|
| Lows below +1.0 ft | 22 | 24 | 36 |
| Daylight windows | 22 | 14 | 24 |
| Daylight minus tides (below 0.0 ft) | 18 | 10 | 9 |
| Deepest daylight low, July | −3.80 ft (Jul 14) | −1.63 ft (Jul 14) | −1.35 ft (Jul 15) |
| Deepest daylight low, all 2026 | −3.80 ft (Jul 14) | −1.88 ft (Dec 24) | −1.65 ft (Dec 24) |
Computed 2026-07-03 from NOAA station 9447130, 9410230, and 8413320 predictions (MLLW).
At Seattle, the −0.5 ft rule barely filters anything: 18 of July's 22 daylight windows are minus tides — 82%. The rule admits most of the month while saying nothing about the days that matter. July 11–16 run six consecutive daylight lows of −2.29 ft or deeper, bottoming at −3.80 ft on July 14 at 11:20 AM, and 2026 as a whole gives Seattle at least eight daylight lows of −2.4 ft or deeper. A Puget Sound tidepooler using the −0.5 rule is a bargain hunter who buys anything under retail.
At La Jolla, the rule earns its reputation. The deepest daylight low of the entire year is −1.88 ft, on December 24. Exactly seven daylight lows in all of 2026 reach −1.5 ft or lower, and July's deepest, −1.63 ft on July 14, is marginal anyway — the low lands at 4:12 AM and only the tail of the window is lit, 79 daylight minutes in all. Against a distribution that compressed, −0.5 ft really does separate a good day from an ordinary one.
At Bar Harbor, the rule mostly misses the point. July has 36 lows below +1.0 ft — more than one per day — but only 9 daylight minus tides, and the deepest daylight low all year is −1.65 ft. Yet Acadia's tidepooling is famous, minus sign or not. The National Park Service pegs the opportunity at "1.5 hours before to 1.5 hours after low tide" — any low tide — and what the station lacks in depth below datum it makes up in sheer vertical travel: the NPS describes "an 8 to 12 foot rise and fall of the seas" happening twice a day, every day.
Why does the same −0.5 ft mean different things?
Three reasons, in decreasing order of importance.
The datum is a local average, and the spread below it varies. A −0.5 ft low is 13% of the way to Seattle's 2026 daylight floor (−3.80 ft), 27% of the way to La Jolla's (−1.88 ft), and 30% of the way to Bar Harbor's (−1.65 ft). Same number, three different percentiles. A threshold only means something relative to what its station can do.
Tide type shapes the counts. NOAA classifies the East Coast as typically semidiurnal — two nearly equal highs and lows a day — while "the U.S. West Coast tends to have mixed semidiurnal tides," meaning two unequal lows. That's why Bar Harbor posts 36 sub-1-ft lows in a 31-day July: both daily lows regularly land near the datum. Seattle posts 22, essentially one a day, because its second low usually sits well above.
Slope does the rest. The same half foot of extra drop walks the waterline a long way out across a flat reef shelf and only a few steps down a steep cobble beach. No datum can tell you that. The station numbers get you to the right day; the beach decides what the day is worth.
So what threshold should you actually use?
| Coast | Worth planning around | Drop everything | Deepest daylight low of 2026 |
|---|---|---|---|
| Puget Sound (Seattle, 9447130) | −2.0 ft or lower | −3.0 ft or lower | −3.80 ft (Jul 14) |
| Southern California (La Jolla, 9410230) | −0.5 ft or lower | −1.5 ft or lower | −1.88 ft (Dec 24) |
| Downeast Maine (Bar Harbor, 8413320) | 0.0 ft or lower | −1.3 ft or lower | −1.65 ft (Dec 24) |
Thresholds are our recommendations; the right-hand column is computed 2026-07-03 from NOAA predictions for each station.
The bars are set so that "drop everything" happens a handful of times a year in daylight. Seattle clears −3.0 ft exactly four times in 2026, all in one run, July 12–15 (−3.16, −3.68, −3.80, −3.49 ft). La Jolla clears −1.5 ft seven times all year. Bar Harbor clears −1.3 ft on six daylight days in 2026, including a tidy July run on the 15th and 16th at −1.35 and −1.32 ft.
Does the right threshold change with the season?
More than most people expect. Seattle's October, November, and December 2026 contain zero daylight minus tides — the deep lows still happen, just at night. Across the whole king-tide season, October 2026 through March 2027, the deepest daylight low Seattle manages is −0.65 ft, on March 25, 2027 at 1:45 PM. A tidepooler holding the summer bar of −2.0 ft would stay home for six straight months; in a Puget Sound winter, −0.5 ft turns out to be a good day after all.
La Jolla runs the other way. August 2026 has just 2 daylight minus tides and September has none, but December has 16, including that −1.88 ft year-best on December 24 at 3:47 PM. Southern California's finest tide pooling is a winter-afternoon sport. Setting a threshold is really setting a percentile, and the percentiles move with the calendar.
How do you find the days that clear your bar?
Not by scanning tide tables for a magic number. The Tide Window Finder computes the hours when a low tide overlaps daylight at any station we track, and stamps each window with an arrive-by time set one hour before the predicted low. The daylight minus-tide index shows the scale of the daylight problem: across our 11 West Coast stations, 2026 holds 940 minus tides, and only 535 of them — 57% — touch daylight. Bar Harbor's tally is 90, with 52 (58%) in daylight. Every formula behind these numbers is on the methodology page.
One closing note, borrowed from the rangers at Acadia because it applies on every coast: "Black rocks and seaweed are especially slippery," and as for the waves, "They're still coming in." In the park, collection is prohibited and animals go back where you found them. The tide that let you out will want the shelf back on schedule.