Long-form field guide · Eight plates · Read in 18 minutes
The Estuary Archive: A Field Guide to Tidal Things
Twice a day the North Sea erases the map and draws it again. This is an index of what returns — birds that read the mud, plants that drink salt, boats built for shallow water, and weather you can taste.
Words & plates · M. A. HarrowSurveyed 2019–2025Tides · 83 observedNo scripts were used to set this page
Where the land negotiates
An estuary is not a place so much as a negotiation. Fresh water arrives believing it is a river; salt water arrives believing it is the sea. For about six miles on the Essex coast neither wins, and in that argument a whole culture grew — of samphire pickers, bawley skippers, eel fishers, and bird counters who set their watches by mud, not by hours.
Walk out at low water and the ground hums. Lugworms turn the flat into braille. Dunlin stitch across it in parties of forty, curlews probe like seamstresses. Above the high-water line, glasswort fattens in the salt pans and sea lavender holds its papery flowers long after colour should have failed. This guide keeps to eight things because eight is what you can learn in one tide.
One term will follow you: sea fretHaar / sea fret: a cold sea fog formed when warm air passes over cold water. It can arrive on a clear day in minutes and erase the far shore. — the haar that rolls in without asking. Fishermen say if you can smell the salt pans, the fret is an hour away. If you cannot see Tollesbury church, it is already here.
The index
Filter the plates. Each entry carries field notes and an enlarged figure. Headings stay in order; nothing is removed for assistive technology — filtered items are hidden from all readers equally.
Showing
Plate 01 · Mudflat
Wading birdsAug – Apr
Dunlin
Calidris alpina · “the stitcher”
A pocketful of pepper thrown across the flat. Dunlin feed in tight, turning ribbons, each bird probing twice a second for ragworm. Watch the back of the flock, not the front — the turn starts there.
Field notes & measures
Length
17–21 cm · bill slightly decurved
Flock
40–400; tight, low, fast
Tide
Best 2 hrs either side of low water
Call
Dry trill, like a rubbed comb
Compare with curlew (Plate 03): dunlin seeks numbers, curlew seeks solitude. If the flock flashes white together, it is nervous — a sparrowhawk is above.
The plant that crunches like the sea. Jointed, translucent stems fatten with salt water and are picked in July, boiled ninety seconds, eaten with vinegar and brown bread. It once fed glass furnaces — its ash made soap and glass.
Field notes & measures
Pick
Late Jun – mid Aug, above mid-tide line
Height
8–25 cm · snap, don’t pull
Salinity
Thrives at 30–35 ppt
Leave
Take tips only; leave roots to seed
Taste raw first: it should be salty, then green, then faintly peppery. If woody, you are a month late.
You hear it before you see it — a long, rising wail that seems to stretch the flat wider. The longest bill of any British wader, curved for deep lugworm. Fewer each year; every winter count now feels like a census and an elegy.
Field notes & measures
Bill
13–20 cm · downcurved, sensitive tip
Wingspan
80–100 cm · slow, gull-like
Best
Solitaries at dawn; listen for “cour-lee”
Status
Red list; do not approach nests
If a dunlin is punctuation, a curlew is a sentence. Give it fifty metres and it will feed as if you were weather.
Built to trawl in water barely deep enough to float. Flat-floored, hard-chined, with a great boom mainsail and a topsail like a handkerchief. At rest they sit upright on the mud as if parked — which, at low tide, they are.
Field notes & measures
Draught
1.2–1.8 m · dries out upright
Rig
Gaff cutter; shrimp trawl astern
Crew
2–3; master, mate, boy
Mark
Red sails, tarred; racing bawleys still meet at Brightlingsea
Stand at the hard at low water and look at the rudder pintles — a century of grounding polished into shine.
A haze of lilac over the high marsh in August. The flowers are papery and hold colour when dried — cottagers hung them over mantels for winter. Bees work it late; the honey from marsh hives tastes faintly of salt.
Field notes & measures
Height
20–50 cm · woody base
Zone
Above mean high-water neaps
Pick
Do not pick wild; grow from seed
Dry
Hang upside down; keeps colour 2 years
Where it grows thick, the ground is safe to walk. Where it stops, the next step is creek — test with a staff.
A string of hoops and funnels that lets an eel in and persuades it to stay. Set at dusk across a fleet, lifted before dawn, the catch silver and furious. A licensed, dwindling art — the eel itself is now critically scarce.
Field notes & measures
Set
Ebb tide, leader 10–20 m into channel
Mesh
8–12 mm; otter guard required
Season
Apr – Oct, no take of silver eels without licence
Return
Release undersize immediately; keep nets clear of seals
Old fishers read eels by moon: dark nights run, full moons rest. Whether science agrees hardly matters at 4 a.m.
The fog that arrives on a sunny day. Warm air slides over a cold sea, cools to its dew point, and the far shore simply unhappens. Sound carries oddly in it — a curlew half a mile off sounds beside you; a ship’s horn sounds underwater.
Field notes & measures
Sign
Wind onshore E–SE, sea < air by 3°C+
Speed
Can advance 1 km in 10 min
Rule
If church vanishes, stop; compass out
Clearance
Often burns off inland by noon, lingers on water
Carry a whistle in haar. Voices vanish; a pealess whistle does not.
On high springs the tide does not creep but arrives — a low, audible push up the narrowing channel, lifting moored boats in order like an audience standing. The old tide tables mark it with a star; the marsh marks it with debris.
Field notes & measures
Range
Neaps ~3.2 m · springs ~5.2 m
Rate
Up to 1 m in 20 min on the fleet
Watch
Two hours before high water; mind causeways
After
Best samphire wash; worst midge hour
Never picnic below the debris line. The tide has already told you, in wrack and feather, exactly how high it intends to come.
Low water, wind NW 3. The flock wheels as one shutter. Press Close or Esc to return to the index — focus returns to the button that opened this figure.
Plate 02 · enlarged
Glasswort, joint by joint
Each segment is a tiny salt battery. Snap the tips, leave the wood. Esc closes.
Plate 03 · enlarged
Curlew at dusk
One bird, one long call, the whole flat listening. Esc closes.
Plate 04 · enlarged
Bawley under sail
Gaff mainsail, topsail, and a trawl astern. Built for six feet of water. Esc closes.
Plate 05 · enlarged
Sea lavender haze
High marsh in August. Do not pick; it holds the sea wall together. Esc closes.
Plate 06 · enlarged
Fyke in section
Hoops, funnels, leader. The eel goes in; the otter must not. Esc closes.
The push up the fleet. Mind the causeway; respect the debris line. Esc closes.
Compare at a glance
One tide, eight answers. Rows align by subgrid where supported; otherwise they fall back to an ordinary grid with the same reading order.
Thing
When
Tide
Note
Dunlin · bird
Aug–Apr
Low ±2h
Flocks flash white
Samphire · plant
Jun–Aug
High marsh
Snap tips only
Curlew · bird
Year-round
Ebb
Give 50 m
Bawley · craft
Apr–Oct sailing
Dries out
Flat floor
Sea lavender · plant
Jul–Sep
High marsh
Do not pick
Eel fyke · craft
Apr–Oct nights
Ebb set
Licence needed
Haar · weather
May–Jul
Any
Stop if blind
Bore · water
Springs
Flood, fast
Mind causeway
Colophon · baseline & fallback
Baseline: semantic HTML, details/summary, native radio inputs with labels, popover + popovertarget, CSS grid and custom properties. That alone gives you filtering, expansion, figures, theming, and the comparison table.
Enhanced where supported::has() drives filtering and theming; container queries reshape cards; subgrid aligns the comparison; scroll-driven animation draws progress and reveal; anchor positioning places the “sea fret” note; @property + color-mix() tint the chrome; view-transition navigation eases anchor travel. Each is wrapped in @supports or ignored harmlessly — without them the page is the same text, simply flatter.
Set in Fraunces and Inter, with Plex Mono for the apparatus. Plates are inline SVG geometry over CSS gradients — no images, no canvas, no scripts. Type is fluid, measure capped at 68ch, motion honoured under prefers-reduced-motion.