Sea swimming

Check the conditions before a sea swim

A useful swimming plan combines the forecast with local knowledge, your experience and what the water is doing when you arrive.

The short versionCheck wind and sea state, tide timing and currents, water temperature, available water-quality information, daylight, entry and exit points, and official warnings. No single green signal makes a swim safe.

What Seyva checks for swimming

The public outlook compares predicted high-tide windows with hourly wind and weather. Its starter swimming setting uses an 11 mph maximum sustained wind and avoids available pollution warnings. That threshold is a product default, not a universal safety limit.

Conditions that can change the decision

  • Wind and sea state: wind can build chop, move you away from an exit point and make the return harder.
  • Tide and current: tide height changes access while moving water can create strong local currents.
  • Cold: colder water and air can reduce the time you can comfortably and safely remain in the water.
  • Water quality: check official bathing-water information and live overflow reports where available.
  • Local hazards: rocks, groynes, piers, boats, surf and rip currents are not captured by a town-level forecast.

Before entering

Choose a lifeguarded beach where possible, swim with someone, identify entry and exit points, wear visible equipment appropriate for the conditions, and carry a means of calling for help. If the conditions do not look or feel right, change the plan.

Read the RNLI’s complete open-water swimming advice.

Written and reviewed by Ollie BartlettFounder of Seyva and a sea swimmer and paddleboarder based near Worthing. Reviewed 14 September 2026. Seyva is a planning aid, not professional safety advice.