Swimming against the tide: can you, and should you?

Could you swim against the tide if you needed to? It's a blunt question for sea swimmers, and if the answer is no, don't swim. But a yes doesn't get a clean bill either. This guide explains why, and how to plan a swim that doesn't rely on the answer.

How fast the sea moves

The Outdoor Swimming Society (OSS) says uninterrupted tidal streams seldom flow faster than about 2 knots, and puts a world-class swimmer's sprint at around 4 knots. Narrow straits can run much faster: OSS lists UK tidal races at around 8 and 10 knots.

The flow isn't constant, either. OSS explains that the most water moves during the middle two hours of the rising (flood) and falling (ebb) tide, so that's when currents are strongest, and they're stronger on spring tides than on neaps.

Rip currents are a separate hazard with their own advice. The RNLI says they usually flow at 1 to 2 mph but can reach 4 to 5 mph, faster than an Olympic swimmer, and that you shouldn't try to swim against one. Rip currents covers what to do instead.

Why a yes still calls for caution

Being able to make headway at the start of a swim isn't the same as being able to do it at the end. A few reasons:

• Swimming against a current wears you out. Swim England warns that fighting a current head-on can rapidly tire you out without making much, if any, headway. The RNLI says strong currents, like those in bad weather and on spring tides, can quickly sap the energy of even the most experienced sea users.
• The cold takes its toll. The RNLI warns that cold water immersion can seriously affect your swimming ability. There's more on that in hypothermia: the signs.
• The water changes while you're in it. Swim England says a current can change direction and speed at different states of the tide, and OSS notes that the actual slack water can differ from the published tide times.
• The wind pushes too. The RNLI points out that wind can push you off course in open water.

The RNLI's advice is short: stay within your depth, and swim parallel to the shore.

Plan the route so the tide does the work

Rather than asking whether you can beat the tide, plan a swim that doesn't need you to. Swim England suggests planning your course so the current works for you: swim out against it, then get a helpful push on the way back. OSS notes that in tidal rivers you can use the speed of the tide to help you swim a distance faster.

That plan only works if you're making steady progress on the way out. If you can't swim against the tide, change your swim, and the sooner you make that call, the closer you are to where you started.

A few more ways to stack things in your favour:

• Time it. OSS says slack water lasts roughly an hour either side of high or low tide in many places, though in some places low tide is the better time, so check locally. Reading a tide table explains how.
• Stay close and parallel. The RNLI's advice is to stay within your depth and swim parallel to the shore.
• Keep it sheltered. OSS advises sticking to sheltered bays unless you understand exactly what you're doing, which means careful planning with a tidal stream atlas, and being extremely wary around exposed coasts and straits.
• Know your second exit. Swim England asks whether the incoming tide will make it hard to get out once it covers the beach you walked over. Know where else you could get out.
• Ask. Swim England suggests talking to local lifeguards, clubs and groups about routes and times to avoid.

Check whether you're drifting

Swim England says recognising that you're in a current takes good sighting. Stop now and then, tread water, and pick two fixed objects on land. Watch how your position changes against them, and adjust your course early. The RNLI adds: keep an eye on your exit point, and make sure you can get back to it.

If the tide's winning

Don't fight it head-on. Swim England's advice is to stay calm, work out which way the current is taking you, and swim at 90 degrees to it to get out of the flow.

If you're tiring, the RNLI says to roll onto your back to rest and hold on to something that floats, like your tow float, then signal for help if you need it. Raise a hand and shout. Swim England notes that three loud blasts on a whistle should get a lifeguard's attention. In the UK, call 999 or 112 and ask for the Coastguard. Who to call if it goes wrong has the detail.

The same question comes up where rivers meet the sea, and tidal rivers covers it there. For tides, rips, waves and the rest of the coast, see the safe sea swimming guide.

Sources

1. Outdoor Swimming Society, Understanding Tides
2. Outdoor Swimming Society, Understanding Tidal Rivers and Estuaries
3. Swim England, How to deal with currents while swimming outdoors
4. RNLI, Open water swimming
5. RNLI, Waves
6. RNLI, Rip currents

This guide is general information, not a substitute for local knowledge or training. Conditions change: check them on the day, and if in doubt, don't go in. Images on the blog are illustrations, not pictures of specific spots.