What is Flounder?
Flounder are hardy flatfish often found in estuaries, harbours and shallow clean-to-muddy ground.
UK sea species guide
Flounder fishing guide
Flounder are hardy flatfish often found in estuaries, harbours and shallow clean-to-muddy ground. Castwise uses species-specific scoring to help shore anglers decide when this target is realistic, where it fits, and what approach to use.
Where do you target flounder from the shore?
Estuary channels, sandy mud, harbour edges, creek mouths and sheltered beaches are common shore options.
How does Castwise help target flounder?
Castwise scores each mark for flounder using tide, season, time of day, wind, swell, pressure, ground, structure, depth, clarity and your logbook, then explains why the window looks strong or weak.
Quick identification and planning facts
Scientific name or group
Platichthys flesus
Single species
High-value planning signal
Estuary channels, mud and sand where a flooding tide covers feeding ground.
Identification cue
A flatfish often showing rough bony tubercles along the lateral-line area.
How to target it from the shore
General UK shore guidance, interpreted mark by mark inside Castwise.
Where to fish
Estuary channels, sandy mud, harbour edges, creek mouths and sheltered beaches are common shore options.
Best seasons
Flounder can be caught across much of the year, with local runs and spawning movements affecting results.
Tide and time
A flooding tide pushing fish over shallow feeding ground is a common window, though local channels can favour either flood or ebb.
Ground and structure
Mud, sand, sandy mud and estuary channels suit flounder.
Bait, lure and rigs
Ragworm, lugworm, peeler crab and small fish or shellfish baits are common on light running rigs or flappers.
Lookalikes and rules
Flatfish are easy to confuse. Check eye side, body shape and markings, and verify before retaining. This is planning guidance, not a legal or biological determination. Before retaining any fish, check the current rules for your nation and local inshore area; for English waters start with the MMO minimum conservation reference sizes and the relevant IFCA.
How Castwise scores flounder
For flounder, Castwise favours estuary context, clean-to-muddy ground, modest depth and tide stages that open shallow feeding routes rather than exposed open-coast swell.
That species-specific result is calculated separately for every mark and window; it is not copied from a generic fishability score. Your logged catches and blanks can then add private evidence about which conditions work for you.
The best target can therefore change by mark and window. Detected safety concerns remain separate from species suitability, but their transparent penalties lower the ranked recommendation; high risk requires acknowledgement and critical risk is non-recommendable.
Responsible use: This is planning guidance, not a legal or biological determination. Before retaining any fish, check the current rules for your nation and local inshore area; for English waters start with the MMO minimum conservation reference sizes and the relevant IFCA. Fish ID is an estimate, forecasts can be wrong, and safety conditions can change quickly.
Sources and latest checks
Species identity and habitat are checked against the Marine Life Information Network (MarLIN). Retention guidance is checked against the current UK MCRS table; local and national rules can be stricter or change during the year. Safety planning should also use the Met Office coast and sea forecast and RNLI angling safety advice. Sources reviewed 15 July 2026.
Frequently asked questions
Can Castwise guarantee flounder catches?
No. Castwise improves planning by matching species, marks and conditions, but fishing scores are guidance, not guaranteed catches.
Can Fish ID confirm this species legally?
No. AI Fish ID is an estimate from a photo. Verify the species yourself and check current local rules before retaining any fish.
Castwise updates
Target flounder with better timing.
Use Castwise for species-specific UK shore fishing recommendations with the factors shown.