Otters have returned to almost every river system in Britain, and yet plenty of people who have walked the same bank for twenty years have never seen one. The animal is not especially rare. It is simply better at this than we are: quick, mostly nocturnal, and capable of slipping past without a ripple worth noticing.
That is encouraging, because it means a sighting is a skill rather than a lottery. Learn what an otter leaves behind, where it likes to travel, and how to sit still at the right hour, and your first one stops being a matter of luck.
Read the signs before you look for the animal
Otter country is written on the bank. Learn the signs on a river near you and you will often find you have been walking through otter territory for years without realising it.
- Spraint. The most useful sign of all. A small, dark, tarry deposit, often glossy when fresh and full of fish bones and scales, left on flat-topped boulders, bridge ledges, log ends and gravel spits — anywhere prominent. A fresh spraint smells faintly of hay or cold tea, with fish underneath. Once you can recognise it, you will start finding otters everywhere.
- Prints. In soft mud or wet sand, look for a broad pad with five toes arranged around it, making a rounded, star-like print — wider than a dog's and usually without deep claw marks.
- Slides. Steep muddy banks often carry smooth, polished grooves where an otter has slipped down into the water, sometimes with prints leading to the top of the run.
- Feeding remains. Fish heads, eel skins and crushed crayfish shells left on a flat stone are classic otter litter. Mink tend to leave messier, more scattered debris.
- Holts and couches. If you find a likely resting place — a gap under tree roots, a rocky bank, a drain mouth — note it and move on. Do not push inside or linger. Otter resting places are legally protected, and disturbance is an offence. If in doubt, check current guidance from Natural England, Natural Resources Wales or NatureScot.
Signs cluster. Where a tributary meets the main river, or where a bridge crosses a deep pool, you will often find spraint, prints and a slide within a few metres of each other. Those junctions are worth returning to.
Read the river like an otter
An otter may use several kilometres of river, but not evenly. It follows the fish, and it follows cover.
Certain features come up again and again: boulder clusters and riffles where fish hold, deep pools with an undercut bank, the tangle of roots beneath an old alder or willow, islands and split channels, the quiet backwater behind a fallen tree. Bridges deserve particular attention, offering deep water and a dry ledge to leave a spraint on.
Walk the stretch in daylight and note those features. An otter working upstream at dusk will tend to move from pool to pool, checking the same rocks and root systems night after night. If you know the route, you can pick a spot on it and wait.
The best hours: dawn, dusk and dirty weather
Dawn is your best chance, with the half hour either side of first light often the peak. Dusk is a close second. In summer, when nights are short and the banks are busy, early morning is almost the only realistic window.
Do not write off daylight entirely. In winter, otters are more willing to be out in the middle of the day, particularly on quiet stretches, in cold snaps and on overcast, drizzly days. Bright, still, hot afternoons are the worst conditions you can pick.
Water levels matter too. Rain and rising water push fish into the margins; a falling river after a spate concentrates them in the pools. On tidal stretches near an estuary, the hours either side of low water are often productive.
Season by season
Late winter and early spring
The best window of the year. Vegetation is down, banks are bare, and otters are active and often travelling in daylight. Signs are at their most obvious.
Spring
Females with cubs are on the move, and cubs can be noisy — a shrill, insistent whistle from a reedbed is worth checking from a distance. Keep well back; a disturbed mother may move her cubs.
Summer
The hardest season. Long days, thick bankside growth and plenty of people on the water. Be on the bank before five in the morning, or choose a quiet stretch with no footpath.
Autumn
Conditions improve quickly. Falling leaves, rising water and, on some rivers, migrating fish bring otters out. Early mornings in October and November can be excellent.
Fieldcraft: how to be invisible
Most failed otter watches fail for one reason: the watcher moves. Otters have sharp hearing and a good nose, and they read a bank full of movement the way you read a headline.
- Walk slowly and stop often. Ten paces, then a full minute scanning ahead, especially 50 to 100 metres up or downstream.
- Watch the water's surface, not the bank.
Photo: Esteban Arango / Pexels
