XTide

XTide provides tide and current predictions. The Apple Watch app and Widget show information for the closest of your favorite tide stations. It is based on the popular open source XTide for Unix from http://www.flaterco.com/xtide/introduction.html
XTide includes a harmonics file (tide data) for the United States only due to legal issues with the data from other countries, but supports custom harmonics files. See https://flaterco.com/xtide/faq.html#60 for more information.
NOT FOR NAVIGATION
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. The author assumes no liability for damages arising from use of this program OR of any 'harmonics data' that might be distributed with it. For details, see the appended GNU General Public License.
(Accurate tide predictions can only be made if the 'harmonics data' for the relevant location are good. Unfortunately, the only way the maintainer of those data has of knowing when they are bad is when someone with access to authoritative tide predictions or observations reports a problem. You should not use this program or any data files that might be distributed with it if anyone or anything could come to harm as a result of an incorrect tide prediction. NOAA and similar agencies in other countries can provide you with certified tide predictions if that is what you need.)
XTide's predictions do not incorporate the effects of tropical storms, El Niño, seismic events, subsidence, uplift, or changes in global sea level.