Direct individual measurements
Largest sea lamprey 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 Main TamarSouth West | 88.6 cm (34.9 in) | 75.5 cm (29.7 in) | 214 | 31 May 2012Gunnislake Weir Index River Fish Trap |
| 2 | River Riding MillYorkshire and North East | 86 cm (33.9 in) | 83 cm (32.7 in) | 3 | 8 Jun 2005Riding Mill Smolt Trap |
| 3 | River OuseYorkshire and North East | 73 cm (28.7 in) | 73 cm (28.7 in) | 1 | 15 Jul 2014Naburn Weir (single anode) |
| 4 | River UreYorkshire and North East | 64.2 cm (25.3 in) | 64.2 cm (25.3 in) | 1 | 10 Jul 2007Westwick |
| 5 | River NiddYorkshire and North East | 64 cm (25.2 in) | 64 cm (25.2 in) | 1 | 20 Jun 2013Nun Monkton |
| 6 | River TemeMidlands | 63 cm (24.8 in) | 63 cm (24.8 in) | 1 | 18 Jul 2014Berrington site 4 |
| 7 | River PerryMidlands | 20 cm (7.9 in) | 20 cm (7.9 in) | 1 | 31 May 2016Wykey |
| 8 | River ArunSouth East | 18 cm (7.1 in) | 16.8 cm (6.6 in) | 7 | 16 Jul 2019Pallingham |
| 9 | River Rye salmon rifflesYorkshire and North East | 16 cm (6.3 in) | 15.5 cm (6.1 in) | 2 | 2 Oct 2016Low Waterholmes |
| 10 | River DoreMidlands | 13.5 cm (5.3 in) | 13.5 cm (5.3 in) | 1 | 16 Aug 2017Abbey Dore Court |
Equal maximum lengths are ordered by sample size. Measurements are shown as recorded and are not converted into estimated weights.
234 fish measured
Measured sea lamprey lengths
The median divides the measured sample in half. This distribution describes surveyed fish, not every sea lamprey living in England.
Only positive individual lengths that pass RiverFish's general measurement checks are included. Each bar covers a 20 mm range.
Latest EA evidence
Latest sea lamprey observations
The ten most recent survey visits that recorded sea lamprey in named waterways.
| Date | River or waterway | Survey location | Fish recorded |
|---|---|---|---|
| 16 Sept 2019 | River Itchen | Mansbridge | 1 |
| 16 Jul 2019 | River Arun | Pallingham | 2 |
| 15 Oct 2018 | Testwood & Nursling Fishery | Wirehouse stream - North Arm | 1 |
| 19 Jun 2018 | River Main Tamar | Gunnislake Weir Index River Fish Trap | 1 |
| 30 May 2018 | River Main Tamar | Gunnislake Weir Index River Fish Trap | 3 |
| 29 May 2018 | River Main Tamar | Gunnislake Weir Index River Fish Trap | 1 |
| 29 May 2018 | River Main Tamar | Gunnislake Weir Index River Fish Trap | 1 |
| 16 Aug 2017 | River Dore | Abbey Dore Court | 1 |
| 20 Jun 2017 | River Main Tamar | Gunnislake Weir Index River Fish Trap | 16 |
| 19 Jun 2017 | River Main Tamar | Gunnislake Weir Index River Fish Trap | 1 |
A survey record confirms sea lamprey at that place and time. It does not show present-day abundance or fishing access.
90 positive survey visits
Survey distribution
EA surveys recorded sea lamprey at 22 locations across 18 named waterways represented on RiverFish.
| Region | Waterways | Locations | Survey visits | Latest record |
|---|---|---|---|---|
| Yorkshire and North East | 7 | 8 | 17 | 2 Oct 2016 |
| Midlands | 5 | 7 | 8 | 16 Aug 2017 |
| South East | 3 | 4 | 5 | 16 Sept 2019 |
| South West | 2 | 2 | 58 | 19 Jun 2018 |
| Anglian | 1 | 1 | 2 | 11 May 1993 |
3 detailed pages
Sea lamprey by river
Open any river-specific page for its measured lengths, largest surveyed individuals, locations and observation history.
Midlands 1 pages
South West 1 pages
Yorkshire and North East 1 pages
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 sea lamprey.
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 →