On the coast: tides, currents, waves

Tides are caused mainly by the pull of the Moon and, more weakly, of the Sun. In many coastal areas there are roughly two high and two low tides a day, and the times shift from day to day. How high the water rises and exactly when differs greatly from place to place, even between neighbouring coves. At new moon and full moon the tides are usually stronger – these are called spring tides.

Rip currents form because waves push water onto the beach, and it has to flow back out somewhere. It takes the easiest path, often a deeper channel between sandbanks, and flows seaward there in a concentrated stream. These currents are usually narrow but can be so strong that even experienced swimmers cannot make headway against them. They do not pull you under, they pull you away from the shore.

Waves do not all arrive at the same size. Among many medium waves a much bigger one can suddenly surge in and wash over rocks, piers or stretches of beach that were dry a moment ago. Then there is cold water: an unexpected fall into it can trigger cold shock, making you gasp for air involuntarily.

Before every beach or coastal walk, check the local tide table – for exactly this place and exactly this day. Tide tables are available from national services, harbour offices, tourist information or on noticeboards on site. Then work out the latest time you must head back, and know the exits from the beach such as stairs or paths. Walking round a headland while the water is rising is one of the classic traps: the way back can be cut off, with a cliff ahead of you.

For swimming, lifeguarded beaches are the best choice. There, swim between the marked areas and pay attention to flags and signs. The meaning of flags can differ between countries, so it is worth reading the explanation on site. Children need constant supervision near water, even if they are only playing at the edge.

Rip currents can sometimes be recognised: a calmer channel between breaking waves, discoloured or murky water, foam or debris drifting out to sea. It is precisely the calm-looking spot that tempts people to swim, and it is still dangerous. If in doubt, ask the lifeguards.

If you are caught in a rip current, do not swim against it towards the shore. Stay calm, float or swim parallel to the shore until the pull eases, and wave and shout as you do. After an unexpected fall into cold water it helps first to lie back and float until your breathing has calmed. The initial cold shock usually passes after a short time, and then you can act more clearly.

If you see someone in difficulty: do not jump in after them. Many helpers end up in mortal danger themselves. Instead, immediately call the local emergency number (112 in the EU) or the coastguard, alert lifeguards, keep the person in sight and, if possible, throw something that floats, such as a lifebuoy, a cool box or a ball. Describe the location as precisely as you can.

Keep away from cliff edges, piers and wet rocks, especially in storms and heavy seas. Watching waves is fascinating, but a single big wave can knock people off their feet. Only go onto mudflats with a local guide, because the rising tide can quickly fill the tidal channels there and cut off the way back.

Tides are highly predictable – which is actually good news. If you know the table, you can plan coastal walks very safely. Wind and air pressure can, however, make the actual water level higher or lower than predicted, especially in storms. So always plan with some margin.

Lakes and rivers have their own risks too: the water can be cold, and rivers have currents and underwater obstacles you cannot see. Swim there only at permitted, known spots.

Rescue organisations such as the British RNLI promote the message “Float to Live” – float first after falling into water. The US weather service gives similar advice for rip currents. These texts do not replace lifeguard training; anyone who wants to help others in the water needs a course for that.