Tides — why low water decides everything.

Why the tide decides everything

A seal does many different things in a 24-hour day: hunting, resting, socialising, moulting, nursing. Almost all of those happen in the water — except resting. For rest, seals need dry land: firm enough to lie on, shallow enough to flee from quickly, and out of the wind. In the Netherlands that means sandbars and mud flats that emerge at ebb.

At high tide, those bars are underwater. The seals are out there hunting or floating. Invisible to you — at most a head briefly breaking the surface. At low tide, the bar comes above water and the animals crawl onto it. Sometimes tens, sometimes hundreds at a time. That is the moment when you can actually see them.

In other words: the whole logic of seal-watching comes down to one question — when is low tide at the place I'm standing?

Twice a day, low water

The tidal cycle averages 12 hours and 25 minutes: after low tide, high tide follows roughly six hours later, and another six hours after that comes the next low tide. So you have two low and two high tides per day. Because the cycle is slightly longer than 12 hours, the low-tide moment shifts forward by about 50 minutes every day. What is low tide at eleven this morning is closer to noon tomorrow, and so on.

The moon is the main cause: its gravity pulls the water around the planet. Wind, air pressure and the shape of the coast affect things locally — what a table says can differ in practice by a few decimetres and a few minutes.

The ideal viewing window

The seals don't all crawl out exactly at the moment of low tide — and they don't all go back in at once either. Count on a window of about two hours before low tide to two hours after low tide for a good chance of viewing. Within that window:

• 2 hours before low tide the first bars start to emerge and the first animals haul out.
• Around low tide itself the largest surface is dry and the most animals are visible.
• 2 hours after low tide the water starts coming back; the animals trickle back into the water.

The practical rule of thumb: time your visit so you're at the lookout around the moment of low tide. If you arrive too late — two hours after low — you may still see a few animals in the water, but far fewer than at the optimal moment.

Spring tide and neap tide

Not every tide is equally strong. Twice a month, around new moon and full moon, the sun and moon line up with the Earth and their pull reinforces — that's spring tide: low water falls extra low, high water rises extra high. Twice a month, around first and last quarter, sun and moon sit at right angles to the Earth and work against each other — that's neap tide: the difference between high and low is smaller.

For seal-watching, spring tide is usually slightly more favourable: more sandbar surface emerges, and sandbanks that normally only briefly break the surface stay accessible as haul-outs for longer. It's not a hard rule — strong wind against the tide can make even a neap tide unusually low, and vice versa.

The tide differs by place and by day

A very important point: low tide is never the same everywhere. The tidal wave travels along the Dutch coast and takes time: between Vlissingen and the Eemshaven the difference can run to several hours. What is low tide at Vlissingen may still be in full ebb at the Engelse Hoek.

So always use a local tide table. Free, official sources:

• Rijkswaterstaat tide tables (rws.nl) — the official Dutch source, per measuring station. Stations relevant for seal-watching include Den Helder, Harlingen, West-Terschelling, Lauwersoog, Eemshaven, Vlissingen, Hansweert and Bath.
• Waterinfo.rws.nl — current and forecast water levels, including graphs.
• Various tide apps that pull in this data (often free for the first month ahead).

Quick calculation: search "low tide {place}"

A practical workflow the evening before your visit:

1. Decide where you'll be watching — for example "Lauwersoog".
2. Search "low tide Lauwersoog [date]" or open the Rijkswaterstaat tide table for that station.
3. Note the low-tide time. For example: 10:42.
4. Plan to arrive about an hour before low tide — in this example around 09:40. You'll catch the first animals crawling out and still have an hour after low to enjoy them.
5. Watch the weather: a strong wind against the tide can push the low up.

A perch on a Friesland dyke, a pair of binoculars and the low-tide time in your head — that's all you need to understand what the Wadden are.

Safety — never walk far onto a sandbar

A dry sandbar looks tempting to walk out onto. Don't, for two reasons.

The seals themselves. You disturb them. An animal that startles and hurries back to the water loses energy that it needs precisely during moulting or pupping. Almost all Wadden and Delta sandbars are protected as Natura 2000 areas; setting foot on them is not allowed in many places.

Your own safety. The tide comes back faster than most people expect. The Waddenzee is notorious for channels that fill in suddenly, and mudflat walkers get trapped every year on bars that looked safe "just a moment longer". Mudflat walking is only allowed in most places under a licensed guide. If you have no permit and no experience: stay on the dyke or close to the beach access, and always keep the high-tide time in mind as your limit. The watchword: better back too early than too late.