Direct individual measurements
Largest flounder by waterway
Ranked by the largest individual measured in EA surveys. The sample size shows how many valid length measurements underpin each waterway's figures.
| Rank | River or waterway | Largest | Median | Measured | Measured at |
|---|---|---|---|---|---|
| 1 | River Rockhampton RhineSouth West | 47 cm (18.5 in) | 13.2 cm (5.2 in) | 30 | 7 Jun 1995The Naite |
| 2 | River HullYorkshire and North East | 45.1 cm (17.8 in) | 14.2 cm (5.6 in) | 92 | 22 Sept 2010Hempholme Lock HULLCRS/(LOWER)1 |
| 3 | River Derwent (Yorkshire)Yorkshire and North East | 40.5 cm (15.9 in) | 19.8 cm (7.8 in) | 94 | 2 Sept 2003Stamford Bridge DERCORS10 |
| 4 | River IdleMidlands | 40.1 cm (15.8 in) | 28.9 cm (11.4 in) | 28 | 4 May 2011Bawtry |
| 5 | River Billinghay SkirthAnglian | 39.4 cm (15.5 in) | 28.4 cm (11.2 in) | 2 | 22 Jul 2004Outfall To Witham (Billinghay) |
| 6 | River FromeMidlands | 38.7 cm (15.2 in) | 7.9 cm (3.1 in) | 233 | 27 Sept 2001Rehabilitation site |
| 7 | River DonYorkshire and North East | 38.5 cm (15.2 in) | 18.3 cm (7.2 in) | 42 | 16 Aug 2017Thorpe Marsh (Tidal) |
| 8 | River IngolAnglian | 38.4 cm (15.1 in) | 8.3 cm (3.3 in) | 16 | 7 Apr 2011Wolferton Pumping Station |
| 9 | River WharfeYorkshire and North East | 37.8 cm (14.9 in) | 16.4 cm (6.5 in) | 342 | 18 Jul 2002Boston Spa |
| 10 | River OuseYorkshire and North East | 37.2 cm (14.6 in) | 15.7 cm (6.2 in) | 221 | 15 Jul 2002Naburn Weir (single anode) |
Equal maximum lengths are ordered by sample size. Measurements are shown as recorded and are not converted into estimated weights.
13,963 fish measured
Measured flounder lengths
The median divides the measured sample in half. This distribution describes surveyed fish, not every flounder living in England.
0–19 mm
7
20–39 mm
605
40–59 mm
3040
60–79 mm
3631
80–99 mm
1689
100–119 mm
1035
120–139 mm
1062
140–159 mm
814
160–179 mm
539
180–199 mm
384
200–219 mm
344
220–239 mm
237
240–259 mm
162
260–279 mm
151
280–299 mm
99
300–319 mm
66
320–339 mm
43
340–359 mm
28
360–379 mm
16
380–399 mm
7
400–419 mm
2
440–459 mm
1
460–479 mm
1
Only positive individual lengths that pass RiverFish's general measurement checks are included. Each bar covers a 20 mm range.
Latest EA evidence
Latest flounder observations
The ten most recent survey visits that recorded flounder in named waterways.
| Date | River or waterway | Survey location | Fish recorded |
|---|---|---|---|
| 14 May 2026 | Well Creek | Salters Lode | 21 |
| 1 May 2026 | River Stiffkey | Upstream Home Farm | 2 |
| 1 May 2026 | River Alt | Alt Weir Downstream | 1 |
| 22 Apr 2026 | River Stiffkey | Warham | 2 |
| 31 Mar 2026 | Counter Drain | Salters Lode | 1 |
| 4 Sept 2025 | River Trent | North Clifton Net | 4 |
| 13 Aug 2025 | Little River Test | Navvy's Shovel, Nursling | 1 |
| 13 Aug 2025 | Testwood & Nursling Fishery | Wirehouse stream - South Arm | 2 |
| 7 Aug 2025 | River Ouse | Naburn - Fry Survey | 6 |
| 4 Aug 2025 | River Don | Doncaster (crimpsal) DON/CO/TEMP/003 | 1 |
A survey record confirms flounder at that place and time. It does not show present-day abundance or fishing access.
1,433 positive survey visits
Survey distribution
EA surveys recorded flounder at 652 locations across 297 named waterways represented on RiverFish.
| Region | Waterways | Locations | Survey visits | Latest record |
|---|---|---|---|---|
| Anglian | 85 | 302 | 671 | 14 May 2026 |
| South West | 76 | 102 | 193 | 31 Jul 2025 |
| North West | 39 | 76 | 126 | 1 May 2026 |
| South East | 38 | 58 | 113 | 13 Aug 2025 |
| Midlands | 31 | 55 | 133 | 4 Sept 2025 |
| Yorkshire and North East | 28 | 59 | 197 | 7 Aug 2025 |
110 detailed pages
Flounder by river
Open any river-specific page for its measured lengths, largest surveyed individuals, locations and observation history.
Anglian 55 pages
Asheldham Brook3 locations · latest 2003Beeleigh Weir Elver Traps2 locations · latest 2023Buck Beck2 locations · latest 2015Bucklesham Mill River1 locations · latest 2016C&B Navigation (Long Pond)3 locations · latest 2004Counter Drain1 locations · latest 2026East Halton Beck FMU2 locations · latest 2021Great Eau FMU4 locations · latest 2015Holland Brook (Main Reaches)5 locations · latest 2014Horsey Mere9 locations · latest 2005Kirby Brook2 locations · latest 1993Lincolnshire Lakes5 locations · latest 1998Louth Canal2 locations · latest 2015New Cut4 locations · latest 1987Old West River3 locations · latest 2003Relief Channel12 locations · latest 2005River Alde (Main Reaches)3 locations · latest 2010River Babingley3 locations · latest 1996River Barton Broad13 locations · latest 2005River Delph4 locations · latest 2011River Ely Ouse3 locations · latest 2006River Fynn2 locations · latest 2017River Glaven2 locations · latest 2017River Heacham3 locations · latest 2008River Heigham Sound5 locations · latest 1998River Hickling Broad12 locations · latest 2015River Holbrook1 locations · latest 2003River Mardyke5 locations · latest 2007River Middle Ouse6 locations · latest 2007River Oulton Broad4 locations · latest 1991River R.Ancholme Subcatchments6 locations · latest 2002River Ranworth Broad6 locations · latest 1999River Rockland Broad4 locations · latest 1991River Salhouse Broad4 locations · latest 1999River South Dike FMU3 locations · latest 1995River South Walsham Broad6 locations · latest 1999River Steeping FMU4 locations · latest 2005River Stiffkey4 locations · latest 2026River Stour4 locations · latest 2024River Thurne (Seine)7 locations · latest 1998River Tidal Ant5 locations · latest 2000River Tidal Bure8 locations · latest 1996River Tidal Waveney13 locations · latest 1999River Tidal Yare29 locations · latest 2010River Welland4 locations · latest 1996River Witham7 locations · latest 2005River Woldgrift Subcatchment5 locations · latest 2013River Wroxham Broad4 locations · latest 2005Roman River (Main Reaches)2 locations · latest 2022South Forty Foot Drain7 locations · latest 2012South Holland Main Drain6 locations · latest 2016Trader/Maud Foster Drain4 locations · latest 2009Waithe Beck FMU3 locations · latest 2018Well Creek1 locations · latest 2026Winterton Beck Subcatchment2 locations · latest 2015
Midlands 11 pages
Blakeney Brook (Blackpool Brook)3 locations · latest 2021Eau2 locations · latest 2017Horsebere Brook2 locations · latest 2012River Cam3 locations · latest 2002River Chelt4 locations · latest 2015River Cone Pill1 locations · latest 2009River Frome3 locations · latest 2024River Idle4 locations · latest 2011River Leadon4 locations · latest 2012River Swilgate3 locations · latest 2021River Trent2 locations · latest 2025
North West 10 pages
River Alt6 locations · latest 2026River Brock2 locations · latest 2017River Douglas4 locations · latest 2016River Gowy5 locations · latest 2014River Lostock10 locations · latest 2018River New Draught2 locations · latest 2013River Wampool3 locations · latest 2021River Wyre5 locations · latest 2016River Yarrow2 locations · latest 2023Savick Brook6 locations · latest 2001
South East 7 pages
River Arun2 locations · latest 2019River Black Sewer2 locations · latest 2012River Great Stour3 locations · latest 2009River Molesey - Teddington2 locations · latest 2023River Ravensbourne3 locations · latest 2008River Roding5 locations · latest 2024Testwood & Nursling Fishery4 locations · latest 2025
South West 16 pages
Brownstone Stream1 locations · latest 2019Eel Survey3 locations · latest 2013Lower Parrett Dredge Surveys6 locations · latest 2014Main Avon Sites4 locations · latest 2024Main River Avon Sites2 locations · latest 2022Main River Axe3 locations · latest 2013River Chestle Pill Rhine3 locations · latest 2013River Frome1 locations · latest 2023River Main Par1 locations · latest 2022River Main Plym1 locations · latest 2025River Main Yealm2 locations · latest 2024River Menalhyl5 locations · latest 2018River Otter Sites1 locations · latest 2023River Piddle1 locations · latest 2025River Rockhampton Rhine3 locations · latest 2017River Taw sites3 locations · latest 2012
Yorkshire and North East 11 pages
Arram Beck2 locations · latest 2016River Blyth2 locations · latest 2024River Derwent (Yorkshire)5 locations · latest 2015River Don3 locations · latest 2025River Hull6 locations · latest 2016River Hull eel surveys5 locations · latest 2025River Northern Burns4 locations · latest 2017River Ouse6 locations · latest 2025River Went3 locations · latest 2017River Wharfe5 locations · latest 2024Streams to Humber2 locations · latest 2025
How to read this page
Survey measurements, not angling records
Environment Agency surveys are designed to monitor fish populations. Their largest measurement is not equivalent to a verified rod-and-line record, and the survey sample does not include every river or every flounder.
Waterway groups with administrative or mixed-river labels are excluded from the headline national totals and rankings. Their eligible river-specific pages remain available in the directory so no published destination is hidden.
The fish records use the Environment Agency source snapshot dated 10 August 2026.
How RiverFish handles the data →