Have you seen these top four Norfolk river species?

The eel was once found in every waterway, but numbers of this fascinating creature have crashed in recent decades. (Image: Archant)

Rivers are always going somewhere, never still, always changing: they ripple, gurgle, ooze and bubble their way towards the sea.

They also have their moods; brown and with a degree of menace after heavy rain in winter spate, all laughter, sparkle and dancing lights in summer when their clear inviting waters wet pebbles and sing splashy, trickling summer songs.

Changeability and movement is their nature and their hypnotic fascination. If like me, you like leaning on bridges or wandering along bank-side paths then you will come to know their wildlife. A river is a fish's world, a kingfisher's hunting ground, an otter's roadway, a swallow's momentary drink and a mayfly's summer dancing ground.

Norfolk's rivers provide a rich, diverse and very special habitat to quite literally thousands of species, some rare and threatened, others widespread and abundant. All fascinating, and all dependent on the quality of the river's water and on its continued flow. Quite literally these are streams of life.

So where to start? And what to look for?

These are four of my favourites. All are present along Norfolk's rivers but none are easy to find. As with much wildlife it's as much a case of them finding you. All you can do is give the river time - and of course hours spent alongside Norfolk's rivers are never wasted. If you move quietly, with eyes and ears open, you are guaranteed some fascinating wildlife encounters. Perhaps a mallard with ducklings, a coot or moorhen quietly brooding their eggs, their nest tucked under overhanging branches, or a gem-like dragon or damselfly dipping into the water, perhaps flying as a tandem pair as they lay eggs onto shallowly submerged water plants.

Kingfisher

Perhaps Britain's most colourful bird, most encounters with this species are a flash of blue, perhaps accompanied by a piercing whistle. Dawn, or at least the first few hours of morning light, seem to provide the best chance of encountering a kingfisher. 'Fly-bys' are memorable, but to sit and watch one dive, catch a minnow or stickleback, then return to its perching post to knock its prey hard a few time to stun or kill it before carefully turning it head first before swallowing it makes a perfect wildlife day.

Otter

Otters are often elusive, shy and nocturnal but not always! Young otter cubs can be playful, reckless and apparently oblivious of a quiet observer. You need luck, and lots of it, but the chances of seeing an otter in Norfolk have never been better. Most views are of a broad, grey-brown head slipping through the water before diving with the long, broad-based tail leaving a 'v'-shaped ripple in the water.

European eel

Eels were once an important local food source and present in such good numbers in some of Norfolk's rivers and coastal marshes that people made a living catching them in nets (eel sets), or spearing them in the reedbeds and marshes with barbed glaves. Norfolk eels were once exported to London in huge numbers but today the species is considered globally endangered. Eels may lack the instant 'wow' factor of kingfisher or otter but the truly mind-bending story of their migration across an ocean to their Sargasso Sea breeding grounds, their strange life cycle, drifting as larvae in the current of the Gulf Stream for nearly a year before returning as glass eels to run up our rivers, at least where sluices, weirs and water-mills still allow passage. Many years later they will desert their settled home on the river for ever to follow the call of the ocean. On wet nights they may even leave the river's course to glide over meadow and field, drawn by the urge to return to the sea and begin their 6,000 km journey to the distant sea of their birth place. Truly amazing.

Water vole

'Ratty', the famous character from 'The Wind in the Willows,' was of course a vole not a rat. Looking rather like an aquatic guinea-pig, rounded, brown and bright-eyed, sadly they are still sometimes killed by people mistaking them for a rat. The first sign that a water vole is near can be the distinctive and very loud crunching, like a child eating a celery stick. The source of the noise will be a water vole sitting on its haunches chewing noisily on cut stems of plants such as water plantain, the stem held neatly between front paws. Though water voles have declined massively, many bankside areas along our Norfolk rivers are still excellent places to spot one. Though if its spots you first then a plop and a few ripples may be the only clue that 'ratty' is still messing about on the river.

David North is Head of People and Wildlife at Norfolk Wildlife Trust