RiverFish

Grayling · Thymallus thymallus

Grayling in the River Mimram

Largest measured grayling: 40.4 cm

The largest grayling measured in Environment Agency surveys of the River Mimram was 40.4 cm, recorded at Tewin flyfishers middle on 8 October 2015.

Across 1,069 measured grayling, the median measured length was 12.8 cm.

RiverFish uses Environment Agency survey measurements rather than rod-and-line angling records. These figures show fish measured during EA surveys of the River Mimram.

See grayling records across England →

Most recent observation25 September 2025Tewin Flyfishers · 31 fish
Largest measured grayling
40.4 cm
Median length
12.8 cm
Fish measured
1,069
Survey locations
9

Individual EA measurements

Largest measured grayling

The largest individual measurements in this river and species dataset. Equal measurements are retained as separate surveyed fish.

LengthSurvey dateSurvey locationSurvey ID
40.4 cm8 Oct 2015Tewin flyfishers middle146933
38.8 cm20 Aug 2024Panshanger quarry166621
38.8 cm8 Oct 2015Tewin flyfishers middle146933
38.6 cm8 Oct 2015Tewin flyfishers middle146933
38.4 cm16 Oct 2018Tewin flyfishers middle154074
36.6 cm8 Oct 2015Tewin flyfishers middle146933
36.4 cm2 Sept 2025Panshanger quarry178396
35.8 cm8 Oct 2015Tewin flyfishers middle146933
35.7 cm8 Oct 2015Tewin flyfishers middle146933
35.6 cm8 Oct 2015Tewin flyfishers middle146933

Lengths are direct survey measurements. RiverFish does not estimate fish weights from length.

Explore the river

Where grayling were found

Each point marks a survey location with at least one grayling record.

Choose a point on the map to see what was recorded there.

Map points are approximate and don’t show fishing access. Check local permissions before visiting.

Place surveyedFirst recordedLast recordedVisits finding grayling
Tewin Flyfishers5 Apr 200725 Sept 202517
Panshanger quarry15 Jun 20062 Sept 202510
Upstream Tewin Fly Fishers3 Oct 20233 Oct 20242
Tewin flyfishers middle8 Oct 201523 Sept 20194
Tewin Archers8 Oct 201523 Sept 20194
Panshanger quarry broadwater bypass channel22 Oct 201021 Sept 20112
Upstream Panshanger weir16 Jun 200616 Jun 20061
School/corn mill13 Jun 200613 Jun 20061
Chandlers End, Mill Farm16 Oct 200316 Oct 20031

Choose a point or table row to see the location. More survey visits can mean more records, but not necessarily more fish.

2003–2025

Survey records by year

Each bar shows how many survey visits recorded grayling that year.

Fish measured by surveyors

Measured length distribution

See how the 1,069 measured fish were spread across different length ranges.

Smallest
6.1 cm
Lower quarter
11.4 cm
Median
12.8 cm
Upper quarter
18.7 cm
Largest
40.4 cm

Lengths are direct survey measurements rather than anglers’ catches.

More fish in this river

Explore the River Mimram

Compare other species with enough survey and measurement data for a detailed page.

Bullhead Brown / sea trout Stone loach 3-spined stickleback Minnow 10-spined stickleback

Before you fish

Good to know

These are past survey records, so the fish present today may be different. Map points are approximate—check local access, permissions and fishing rules before visiting.

Learn how RiverFish uses the data →