How to spot signs of otters along rivers

Why otter signs matter

Otters are among the UK’s most exciting river mammals, but they are also among the hardest to see. They are mostly nocturnal, shy, and travel long stretches of water. That is why signs matter. A fresh spraint, a muddy footprint or a pile of fish bones can tell you that an otter is using a stretch of river, even if the animal itself stays hidden. For conservationists, these clues are gold dust: they help map otter ranges, identify important feeding and resting places, and show whether improvements to water quality, bankside planting or fish passage are working.

Spraints: the otter’s calling card

Spraints are the most reliable sign. These are otter droppings, and otters often leave them in prominent places: on boulders midstream, on bridge ledges, at the base of trees, on fallen logs, or beside paths along the bank. A fresh spraint is dark, glossy and tarry, and it usually has a distinctive musky smell—often described as fishy, sweet and slightly like jasmine. Look closely and you may see fish scales, small bones, or fragments of crayfish shell. Older spraints dry to a pale grey or brown and crumble easily. Because otters use the same sites again and again, a rock or bridge support with several spraints is a strong clue that a territory is active. Do not touch them; leave them for the next otter and for other recorders.

Footprints and tracks in mud

After rain, soft mud and silt become a natural notebook. Search along the water’s edge, on gravel bars, under bridges, and at the mouths of side streams. Otter footprints are broad and rounded, with five toes and a wide pad. They often measure around 5–7 cm across, though size varies. You may also see claw marks, especially in soft ground, and sometimes a drag mark where the tail has brushed the mud. Mink prints are smaller and more pointed, while dog prints are usually rounder and do not show the same wide, star-like spread of toes. Look for tracks in pairs or groups, often heading purposefully along the bank or into the water. Early morning is best, before rain, walkers or livestock erase the evidence.

Feeding remains, slides and holts

Otters are messy eaters, and their leftovers are another giveaway. On flat rocks, logs or grassy banks, you may find feeding remains: fish skeletons, loose scales, crayfish claws, frog bones, or feathers. They often eat the middle of a fish and leave the head and tail. You might also spot a slide: a smooth, muddy chute down a steep bank into the river, created by otters repeatedly sliding in. These are especially obvious on soft earth after rain. More secretive are holts—underground dens among tree roots, rock crevices or old rabbit burrows—and couches, which are above-ground resting spots in dense reeds or long grass. Holts are legally protected, so never enter, dig into, or block one. If you find a suspected holt, note it from a distance and move on quietly.

Reading the river: where to look first

Otters follow reliable routes. Start where water is clean, food is plentiful, and banks offer cover. Good places include bridge arches, confluences where two streams meet, islands, pool tails below riffles, weirs, and wooded banks with exposed tree roots. Check the tops of large boulders, the aprons of bridges, and any flat ledge that sits above the water. Look for runs—narrow, flattened paths through vegetation along the bank—and for spraints placed as territorial markers. In winter, when banks are bare, signs are often easier to spot. In summer, dense growth hides them, so focus on mud and stone. A slow, quiet walk of a few hundred metres, repeated over weeks, will teach you more than a long rushed survey.

Searching responsibly and helping conservation

Watching for otter signs is a privilege, and it should never come at the otter’s expense. Use these practical rules:

• Keep your distance from holts and couches, especially between February and August when cubs may be present.
• Keep dogs on a lead near rivers and never let them enter dense bankside cover.
• Avoid repeated trampling along the same muddy margin, as this can erode banks and disturb resting places.
• Record what you find—date, location and type of sign—and pass details to your local biodiversity records centre or wildlife recording group.

These records help build a picture of where otters are thriving and where they need help. Conservation work such as reducing pollution, restoring bankside trees, improving fish passage and protecting wetlands all support otters. So next time you walk a river, slow down, look for the clues, and enjoy the quiet thrill of knowing an otter has passed that way.