A little help by the water.

Choose a place

Use Places to choose a tide station, or allow location access to find the nearest one. Location is optional. If a beach or city does not appear in search, try the nearby port or station name, or browse the map. Coverage is by station, not every point along the coast.

If the nearby place seems wrong, check Waterline’s location permission in iPhone Settings, reopen the app, or choose a station manually. A geographically close station can still be on a different coast or in a different tidal system.

Tide sources and coverage

Waterline covers the United States and its territories with NOAA’s tide predictions. Outside the US it includes NOAA’s own stations at a few ports, and places in Japan, France, New Zealand, Norway and Queensland, Australia, where the tides come from the national agency or were checked against its tables. Places elsewhere are left out until their tides can be checked against an official source. In Settings → Tides at [your place], check the source, height reference and any notes for that station. Where the data comes from includes source links, licences and acknowledgments.

Where the numbers come from

• NOAA CO-OPS supplies downloaded tide predictions. It also supplies tidal-current predictions and water-temperature observations where available.
• International tides are calculated on your device from TICON-4 harmonic constants derived from GESLA-4 observations, plus data from LINZ in New Zealand, Kartverket in Norway and JMA for Kobe and Osaka.
• Heights abroad are measured from each country’s own reference: JMA’s tide-table levels in Japan, Shom’s chart datums in France, LINZ’s and Kartverket’s chart datums in New Zealand and Norway, and Maritime Safety Queensland’s lowest astronomical tide.
• NWS provides US forecasts and available marine/coastal warnings. MET Norway provides worldwide weather and extends forecast coverage. Waves, currents, water temperature and warnings are not available everywhere.
• Where no sensor is near, the water temperature is a satellite estimate from NASA JPL’s MUR sea-surface temperature analysis, served by NOAA CoastWatch. Waterline marks it as an estimate.

Why heights or times can differ

Compare the same station, date, time zone, units and height reference. NOAA heights use mean lower low water (MLLW); other stations may use a different zero. Waterline joins downloaded NOAA points into a curve and calculates international predictions from harmonic constants. A nearby station or another provider may use different inputs.

Not for navigation. These are astronomical tide predictions. They do not include storm surge, river flooding or wind-driven changes in water level. Use official local forecasts, charts and warnings for safety decisions; Waterline alerts are not emergency warnings.

Set up alerts

Open a place on Now and tap its bell. Choose the tide or condition, any height or threshold, and when to be notified. Review the preview, save the rule and allow notifications. Each place has its own alerts.

If an alert does not arrive, confirm the rule is enabled, check Settings → Notifications → Waterline, and review Focus and Scheduled Summary. Check any daylight-only restriction and the station’s time zone. Wind, wave and water-temperature rules need the relevant data to be available.

Open Waterline regularly with an internet connection to update forecasts and refill scheduled alerts. The app schedules upcoming notifications locally and requests background refresh, but iOS decides when background work runs. Delivery and forecast freshness are not guaranteed when the app has not refreshed.

Home Screen and Lock Screen widgets

1. Open Waterline once and select a place.
2. On the Home Screen, touch and hold an empty area, then choose Edit → Add Widget and search for Waterline.
3. For a Lock Screen widget, touch and hold the Lock Screen, choose Customize → Lock Screen, then add Waterline under the clock.
4. Touch and hold a Home Screen widget and choose Edit Widget to select another place or the nearest station. Edit Lock Screen widgets while customizing that screen.

If a widget is stale, open Waterline with a connection and confirm its selected place. For a nearest-place widget, check location access; it may fall back to the last nearby station. iOS controls refresh timing. If needed, remove and add the widget again. See Settings → Widgets in Waterline for previews.

Live Activity and Dynamic Island

In Waterline’s Settings, open Lock Screen and Dynamic Island (or Lock Screen on models without Dynamic Island). Start the activity for the place you are viewing. It can follow the tide, wind, sun or moon. You can also manage it from the place’s bell sheet.

Allow Live Activities for Waterline in iPhone Settings. iOS ends a Live Activity after eight hours; Waterline can start it again when you reopen the app if you enable that option. The activity is separate from a permanently added Lock Screen widget. If it stops updating, reopen Waterline, refresh its data and start the activity again.

Apple Watch and complications

The Watch app works with the iPhone app, so install Waterline on your iPhone first. Then open the Watch app on your iPhone and install Waterline under Available Apps if it is not installed. Open Waterline on both devices and select the place on your iPhone. The Watch receives that selection and cached tide and weather data; it can also fetch data when connected.

To add a complication, touch and hold the watch face, tap Edit, swipe to complications, then select a compatible slot and choose Waterline. Available complications depend on the face and slot.

If the Watch shows an old place or stale conditions, check that it is paired and connected, open both apps, and let the phone refresh. Cached tides can remain available offline, while weather and observations need an updated connection. watchOS controls complication refresh timing.

Offline use and missing conditions

International tides are calculated from data bundled with the app. NOAA predictions need an initial download; saved predictions are then available for the period downloaded. Forecasts and observations can be missing, stale or out of range offline.

If a value is missing, check your connection, reopen the place and check its source notes. A dash can mean the provider has no data for that place or time. The absence of a weather-warning banner does not mean conditions are safe.

For Siri, try “Next tide in Waterline”, or name a place you follow. Waterline’s actions also appear in Shortcuts; setup examples are in Settings → Siri and Shortcuts.

Settings, saved data and privacy

Your followed places, names, alert rules and preferences are stored on your devices. Waterline has no account-based sync. Reinstalling can lose local data and is not the first troubleshooting step; Keychain, Watch or backup copies may persist separately.

Read the Privacy Policy for location access, provider requests, Apple services and deletion choices.

Support instructions checked against Waterline 1.0, build 97 · October 25, 2026.