"Check the moon before you go" is some of the oldest advice in fishing, and it's also one of the most overstated. Some of it holds up. Some of it doesn't. This page walks through both halves honestly, so you can use it the way it actually deserves to be used — as one more thing worth a glance, not a guarantee.
Two different "moon" things, explained
People usually mean one of two different things when they say "the moon affects fishing," and mixing them up is where a lot of the confusion comes from.
Moon phase
The roughly 29.5-day cycle from new moon to full moon and back. The popular belief is that fishing picks up around new and full moons, when the sun, earth, and moon line up and produce the biggest tidal swings ("spring tides"), and slows down around the quarter moons, when tides are weakest ("neap tides").
Solunar periods
The moon's position in the sky on any given day. As it crosses overhead and then underfoot roughly once each per day, solunar theory predicts two major periods (about two hours each, centered on those moments) when fish feed hardest. Moonrise and moonset are said to trigger two shorter, weaker minor periods in between.
Both ideas get bundled into the same "solunar table" you'll see in most fishing apps, ours included. It's worth knowing they're doing two different jobs: one predicts a good week, the other predicts a good two hours within a day.
Where it's solid: real tides
The moon's gravity genuinely pulls on the earth's water, and in any body of water connected to the ocean, that produces a real, measurable tide. A moving tide pushes baitfish around, stirs up food, and gives predators an easy reason to feed harder — that's straightforward, well-understood physics, not a theory in the shaky sense.
Lake Saroma and Lake Ogawara specifically, since both are brackish lagoons physically connected to the ocean. Saroma's water is close to full seawater salinity, so a real tide moves through it. For these two, checking whether a major period overlaps with a moving tide (not high or low slack water) is the more defensible version of "solunar timing" — closer to just reading the tide.
Where it's shakier: freshwater lakes
Lake Biwa, Kasumigaura, Inawashiro, and Suwa are effectively closed bodies of freshwater. There's no ocean connection for the moon to create a tide with, and the moon's direct gravitational pull on a lake that size is far too small to move any meaningful amount of water. So whatever effect the moon has here, it isn't the tide mechanism — it would have to be something else, like fish responding to changing light levels at night, or an internal biological rhythm, both of which are much less established ideas than "the moon moves water."
This is the part of solunar theory that rests more on tradition than on a demonstrated physical cause. That doesn't mean it's wrong — plenty of long-standing angling knowledge isn't formally proven either — just that it's a different kind of claim than the tide-driven version above.
What the actual research says
The version of solunar theory most anglers use today comes from John Alden Knight, who developed it in the 1920s and 30s after reviewing roughly 200 record-catch reports and noticing a pattern. That's an interesting observation, but it's his own informal analysis, not a controlled study.
Since then, the picture from actual research has stayed mixed. One review covering around 190 studies on pelagic species found just over half showed fish swimming deeper as moonlight increased, only about 5% showed the opposite, and the response varied a lot by species — not a clean, consistent "more moon means more feeding" story. Where correlations between moon phase and catch rate do show up in commercial fishing data, the direction is often inconsistent even within closely related species.
Critics also point to a simpler, more mundane explanation for why solunar tables often "work": major periods frequently land near dawn or dusk, which are already reliably good fishing windows because of light levels, regardless of the moon. And there's a well-documented confirmation bias at play — anglers tend to remember the trips where a major period lined up with a good bite, and forget the ones where it didn't.
How to actually use it
None of the above means solunar timing is useless — it means it deserves to be one input, not the deciding one.
- Treat it as a tiebreaker. If you've already got the day off and the weather looks decent, checking whether a major period lines up with dawn or dusk is a reasonable bonus to plan around.
- Don't cancel a trip over a "poor" rating. Weather, water temperature, season, and being on the right lake for the right species (see the six lakes we cover) all matter more, especially on the four freshwater lakes here.
- On Saroma and Ogawara, check the actual tide. A major period during a moving tide is a more meaningful combination there than the solunar table on its own.
- Stack your conditions. The best realistic case is a major or minor period that happens to overlap dawn or dusk, stable barometric pressure, and the right season for your target species — not moon phase carrying the day by itself.
In short: worth a look before you head out, alongside the weather — not a reason to stay home, and not a substitute for fishing the right lake at the right time of year.
Made by us
Tsurerukana?
We also build an app that scores major and minor feeding windows for each of the six lakes on this site using solunar theory — worth checking alongside the weather, not a guarantee — plus a lure-matching suggestion for what's likely working right now. Get it on Google Play →