How to identify freshwater wildlife

A spring riverside stroll reveals fresh arrivals and newly emerged animals. Use our handy guide to look out for 11 species and the telltale signs left by a twelfth – the otter. 

All illustrations by Dan Cole/The Art Agency

All illustrations by Dan Cole / The Art Agency

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1 Common sandpiper Actitis hypoleucos

18–20cm. Summer visitor; arrives in March–April. Nests on fast-flowing rivers, mainly in north and west.

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2. Sand martin Riparia riparia

12–13cm. Summer visitor; arrives in March. Told from house martin by chest band. Nests in sandy banks.

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3. Goosander Mergus merganser

58–68cm. Fish-eating ‘sawbill’ duck with long serrated bill. Nests on fast-
flowing rivers in north and west.

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4. Otter prints & spraint Lutra lutra

Prints: five toes (not four as in foxes or dogs) above large pad mark. Spraint: smells sweet, not fishy like mink.

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5. Bullhead/Miller’s thumb Cottus gobio

Up to 8cm. Fat, flat-topped head; large pectoral fins at sides. Hides near stones in well-oxgenated rivers.

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6. Minnow Phoxinus phoxinus

Up to 5cm. Slim, with dark mottling along flanks. In shallows, often in large shoals when spawning.

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7. Water moss Fontinalis antipyretica

Long stems up to 20cm in length; UK’s largest aquatic moss. Attaches to stones or submerged tree roots.

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8. Opposite-leaved golden saxifrage Chrysosplenium oppositifolium

Creeping plant with tiny gold flowers. On damp riverbanks, often in woods.

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9. Butterbur Petasites fragrans

Pink flower spikes appear March–May, before huge round leaves unfurl. On damp riverbanks, often in woods.

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10. Alderfly Sialis lutaria

10–15mm. Brown, strongly veined wings. A sluggish fly with weak flight; often rests on waterside vegetation.

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11. Large dark olive Baetis rhodani

Body: 8–12mm; tails: up to 18mm. On wing January–April. Abdomen grey (male) or red-brown (female).

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12. River skater Aquarius najas

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13–17mm; larger than common pond skater. Floats on surface film of rivers, mainly in north and west.