Flounder

By Alex Clayton · Updated 23 October 2026

The flounder is a sea fish that regularly swims into fresh water. The Canal & River Trust has recorded it at Diglis Fish Pass, well up the Severn near Worcester.

The flounder fish (Platichthys flesus), also called the European flounder or fluke, is a small flatfish common around Britain and Ireland. It lives in estuaries, tidal rivers and sheltered shores, and it takes worm baits on simple bottom tackle, often on the flooding tide.

This guide covers identification, where and when to find it, tactics, and the size rules by district.

Flounder at a Glance

These are the essentials, checked against IFCA, Canal & River Trust and Wildlife Trusts sources in October 2026.

Fact	Detail
Scientific name	Platichthys flesus
Other names	European flounder, fluke
Typical size	About 30cm and 2lb 3oz (1kg)
Maximum length	Up to 50cm
Listed record weight	5lb 11oz 8dr (about 2.59kg)
Lifespan	About 15 years
Diet	Worms, small mussels and other molluscs, amphipods and other crustaceans, gobies
Habitat	Estuaries, sheltered shores, tidal and lower freshwater river reaches
Spawns	At sea, late winter to early summer
Conservation status	IUCN Least Concern
Minimum size	Depends on the IFCA district (see the minimum size section)

There is no single UK minimum size, so that line gets its own section below.

How to Identify a Flounder

Orange spots are the least reliable clue on a brown flatfish, because a dab can show them too. Run your finger along it instead.

Feel it first. The most useful check: a flounder has hard, rough tubercles along the front half of the lateral line and at the dorsal and anal fin bases on the eyed side.
Shape and colour. Oval body, small mouth. The eyed side is dark green, olive or yellowish-brown, sometimes faintly orange-spotted. The blind side is pale.
Eye side. Flounder are usually right-eyed, but reversed (left-eyed) fish turn up, so eye side alone proves nothing.
Hybrids. Flounder and plaice interbreed (Wildlife Trusts), so some fish cannot be named with certainty on the bank.

If the flounder fish in your hand feels rough in those places, assume flounder, then rule out plaice using the next section. For other species, see our fish identification guide.

Flounder vs Plaice, Dab and Sole: How to Tell Them Apart

The quickest way to separate a flounder from a plaice is a row of bony bumps you can feel behind the eyes.

Planet Sea Fishing’s flatfish guide describes a row of 4 to 7 bony knobs running from the upper gill opening towards the eyes on a plaice. Flounder lack them. Both dab and flounder can show orange or red spots, so spots alone do not make a fish a plaice.

Feature	Flounder	Plaice	Dab	Sole
Feel of eyed side	Rough tubercles along lateral line and fin bases	Smooth	Not a reliable check	Not a reliable check
Head	No bony knobs	4 to 7 bony knobs behind the eyes	No knobs	Small eyes, rounded snout, mouth curving round to the side
Lateral line	Fairly straight	Fairly straight	Sharply curved over the pectoral fin	Straight
Spots	Sometimes faint orange	Usually bright orange	Can show orange spots	None distinctive
Body shape	Oval	Oval	Smaller, oval	Elongated, tongue-shaped

Getting flounder vs plaice right matters because plaice and sole carry their own size limits in some districts. Kent & Essex IFCA and Eastern IFCA, for example, list plaice at 27cm and sole at 24cm.

The short version: rough to the touch with no head knobs, flounder. Knobs and bright spots, plaice. A curved lateral line, dab.

Where and When: Estuaries, Tidal Rivers and the Winter Move to Sea

Some anglers swear flounder are a winter fish. Others say spring to autumn. Both can be right, depending on where you fish, and the reason is the spawning run.

Habitat

Flounder live in estuaries, sandy and muddy sheltered shores, creeks and tidal rivers, and they push up into fresh water. The Canal & River Trust describes them as common in the Severn and Dee estuaries.

The yearly cycle

In winter, adults move to deeper, warmer water (North Western IFCA) and spawn at sea. The Canal & River Trust gives February to May at 20 to 40m depth. North Western IFCA says usually March to June.

Juveniles enter estuaries in early May. Males mature at about 3 years and females at about 4.

What this means for anglers

Fish feeding before the spawning run can give good estuary sport. Sea Angler reports catch rates rising at night, dawn and dusk from autumn into mid-winter. A local report from Hilbre on the Wirral describes flounder as plentiful there from April to October.

These are regional reports, not a national rule. Flounder hunt by sight, and North Western IFCA says they feed mainly in daylight, which does not sit neatly with the night advice. A local tackle shop or club will know which months fish best on your estuary.

Flounder fishing in the UK suits anglers with an estuary within reach. Away from estuaries and sheltered sand, look at other UK flatfish instead.

Flounder Fishing in the UK: Tides, Baits and Rigs

Fish the first of the flood. Flounder push up over the flats and into creeks as the water covers them.

Tide timing. Sea Angler, drawing on Dr Roger Munro’s advice, gives three windows: the start of the flow on a neap tide, around high water, and midway down the ebb.

Rig. Use a one to three hook paternoster or a flapper with long snoods, and hooks from size 6 up to size 1. Fish a grip lead where the tide runs and a plain flat lead on clean, slack ground.

Baits. Sea Angler suggests:

harbour ragworm in mid-estuary creeks
lugworm on surf beaches
peeler crab for bigger fish
razorfish and mussel
a sliver of mackerel added to the hook

Presentation. Fish a slack line and move the bait now and then to cover gutters and ridges. Flounder often shoal, so one bite usually means more fish nearby.

Tidal rivers and fresh water. The Canal & River Trust suggests basic swim-feeder tactics with worms or maggots on the bottom, on finer line and smaller hooks. On freshwater reaches, check whether you need a rod licence: see our fishing licence guide.

Safety. Estuary gullies fill fast on the flood, and the Hilbre report rates neap tides as safer. Check tide times and your route back before you walk out.

If you are new to it, start with harbour rag on a two-hook flapper over the first two hours of a neap flood.

Flounder Minimum Size: It Depends Where You Fish

Search for the flounder minimum size and you will usually get one number. There is no single UK figure. North Western IFCA notes there is no EU minimum size for flounder, so in England each Inshore Fisheries and Conservation Authority (IFCA) sets one by byelaw, or does not.

District	Flounder minimum size	Source
North Western IFCA	25cm (250mm), applies to all persons fishing in the district	NWIFCA species page, Byelaw 1
Cornwall IFCA	25cm (the list does not cover some rivers and estuaries in the district)	Cornwall IFCA recreational page
Kent & Essex IFCA	None listed in the minimum sizes byelaw	Kent & Essex IFCA minimum sizes
Eastern IFCA	None listed in the finfish table	Eastern IFCA minimum sizes
Devon & Severn, Sussex, Southern, Northumberland, North Eastern IFCAs	Check the district’s current byelaw	For example, Southern IFCA minimum sizes
Wales, Scotland, Northern Ireland	Check with the Welsh Government, the Scottish Government’s Marine Directorate or DAERA

“None listed” means no flounder entry in that table when checked in October 2026. Rules change, so confirm before you keep a fish.

The Angling Trust’s guidance list gives 27cm as the highest legal figure and 30cm as the size at maturity, and says the byelaw of the IFCA where you caught the fish takes precedence. That 27cm does not match the 25cm in the North Western and Cornwall byelaws.

A sensible voluntary standard is to return any flounder under that 30cm maturity size. Check your district IFCA site before you keep one, and if in doubt, put it back.

Handling, Returning and Eating Flounder

A flounder is small and flat, so it is one of the easier sea fish to unhook and return quickly.

Wet your hands, support the body and unhook fast, with forceps or a disgorger on small fish. Return it at the water’s edge, not from height. North Western IFCA notes that anglers usually target flounder as catch and release.

The flesh is white and delicate, but a typical 30cm fish gives limited meat, and flounder are not commonly sold to UK consumers. Keep one only if it is legal under your local minimum size and you will eat it fresh.

Frequently asked questions

What is a flounder called in the UK?

In the UK it is the European flounder, and North Western IFCA also lists the name fluke. In North America, "flounder" and "fluke" are used for other flatfish species, so many recipes and guides online describe a different fish from the one caught in British estuaries.

What is the British record flounder?

The Canal & River Trust lists the record flounder at 5lb 11oz 8dr (about 2.59kg). Other sources give differing details, and the British Record (rod caught) Fish Committee keeps the official list, so check there for the current record and its details.

Is flounder good to eat?

Yes. The meat is white and delicate, though a small fish yields little of it, and you rarely see flounder in UK shops. Only keep a fish that meets the size rule for your district, set out in the minimum size section on this page.

Can flounder live in fresh water?

Yes, for part of their life. Flounder run up tidal rivers and lower freshwater reaches, and have been recorded as far inland as Diglis Fish Pass near Worcester on the Severn. They spawn at sea, so you will not find them breeding in rivers.