Support

Have a question or found a problem? Email slackwater@openwaters.io. A person reads it. You do not need an account or a Premium purchase to ask for help.

For a problem with a prediction, include the station name, date, time and time zone, what you expected, and a screenshot if possible. Your app version, device and iOS version help us investigate other problems.

Frequently asked questions: downloads and offline use, finding places and reading predictions, devices and privacy, and free features and Premium.

Downloads and offline use

Does Slackwater work without an internet connection?

Bundled stations work offline from first launch. Canadian stations need an initial download. Most then calculate predictions on your device without an expiry date; some Canadian current stations store a limited period of published predictions instead. Their pages show how long those predictions are available offline.

Open the places you need and check their download status before leaving signal. If you use the map, check that the charts you need are downloaded too.

What does "Available offline for 20 more days" mean?

It means the saved current predictions cover that many more days. When that coverage runs out, you need an internet connection to download more predictions for that station. Other stations with on-device predictions continue to work offline.

Do I have to download those current stations again myself?

Slackwater automatically fetches more predictions for stations in your download set when you open the app with a connection and the saved coverage needs extending. You do not need to select those stations again. Keep the app open while downloads finish; a refresh needs internet access.

Before a trip without service, you can also open a current station and tap Refresh near the bottom of its page. Downloads cover about a month. Check the date shown after refreshing, rather than assuming every station has the same coverage.

What happens when I travel beyond the 150 km download area?

The Within 150 km choice follows your location. With location access enabled, opening Slackwater in a new area adds nearby Canadian stations to your downloads when you have a connection. Previously downloaded stations stay saved.

You can also search for a place and open it to download its predictions before travelling there. You do not have to wait until you arrive.

How do I download more Canadian stations?

Open Downloads near the bottom of the main list. The choices include Nearby, Within 25 km, Within 150 km, and All current stations. Select the coverage you want, then check that the downloads finish before going offline. Opening an individual station also starts its download.

Why does a download say "Queued", "Retrying", or "Waiting for signal"?

Downloads run in order, so a queued station is waiting its turn. Slackwater retries temporary failures automatically. If it is waiting for signal, reconnect to the internet and reopen the app. The Downloads screen shows progress and offers a retry action when downloads fail. If a station keeps failing, email us its name and the message shown.

Finding places and reading predictions

What can I use Slackwater for?

Check high and low tides, current speed and direction, and slack-water times for a beach visit, fishing trip or passage. Move through the timeline to see a chosen time, or read the schedule below it. Sunrise, sunset and moon information help put the day in context.

Predictions are not observations. Weather and river flow affect conditions. Slackwater is not for navigation.

Where does Slackwater have coverage?

Tide stations are available around the world; current stations cover the US and Canada. Coverage varies by place. Search in the app or browse the station directory to check your destination. The website and app do not have identical coverage, so check the app before a trip.

Can I find a station without sharing my location?

Yes. Search by name or browse the map. Location permission is optional; it helps Slackwater find nearby stations. If the nearby list is centred on the wrong place, check location access in your device's Settings, then reopen the app. You can still search while location is unavailable.

Why are high or low tide and slack water at different times?

High and low tide describe water height. Slack water describes the tidal current slowing and changing direction. They do not necessarily happen together, especially in narrow passes. Use a current station for current speed and slack times, rather than assuming the tide station tells you when a pass is slack. Read what slack water means and how tides work.

Why does a prediction differ from what I see on the water?

Tidal predictions describe the expected tide or tidal current, not every influence on the water. Wind, air pressure, river flow and local conditions can change what you observe. Different sources may also use different stations, time zones or height references. Check the station, date, time zone and units when comparing predictions.

If something still looks wrong, email us the details and the source you are comparing against. The accuracy report explains our checks and their limits.

What if a station is missing or says predictions are unavailable?

Try searching for a nearby place. A listed station does not always have usable prediction data, and an unavailable prediction cannot be fixed by purchasing Premium. Send us the station name or location so we can investigate a coverage question.

Devices and privacy

Which devices does Slackwater support?

Slackwater runs on iPhone and iPad with iOS or iPadOS 26 or later, and Apple Watch with watchOS 26 or later. Download it on the App Store.

Do I need an account? Where is my data stored?

There is no Open Waters account, password or login to reset. Downloaded predictions and settings are stored on your device. Favorites and preferences can sync through Apple's iCloud. Your GPS coordinates stay on your device. The privacy policy explains online requests, iCloud and purchases.

Is the app open source?

Yes. The app source is public. You can ask questions and report problems by email without a GitHub account.

Free features and Premium

What is free, and what needs Premium?

Tide charts, current predictions, station search, favorites, home screen widgets and the Apple Watch app are free, with no ads. You can choose any prediction date without a subscription. Canadian prediction downloads do not require Premium.

Optional Premium adds alerts, station calendars, lock-screen widgets and Apple Watch complications. Annual and lifetime purchase options include the same Premium features. See pricing and purchase terms for details; Apple shows your local price before you confirm a purchase.

How do I restore a Premium purchase?

Open Support Slackwater from the main list or Settings, then choose Restore purchase. Use the Apple account that made the purchase. If Premium is still unavailable, email us with your app version and what the purchase screen shows.

How do I manage or cancel the yearly subscription?

Manage or cancel it in your Apple account's subscription settings. The yearly subscription renews automatically until cancelled. Lifetime is a single purchase with no renewal. Cancelling a subscription does not require deleting the app.

Still need help? Email slackwater@openwaters.io.