Britain's otter population began to plummet in the 1950s. Hunters were blamed but the single biggest factor was the pollution of our rivers and streams through chemicals.

In Wales this might have been due to sheep dip and in other parts of the country through herbicides and pesticides. Being at the top of the food chain, otters were particularly vulnerable to the build-up of toxins.

Hunting was outlawed in 1981 and the use of chemicals is much more tightly controlled. Slowly the waters cleared and eventually the otters staged a comeback. Nowadays otters are present on 90% of Welsh rivers but there's still a long way to go. It'll take a hundred years for the population to recover to its pre-1950 level.

Apart from clean water, otters need food with lots of protein to fuel their hyperactive bodies and to endure the cold water. An otter will eat 15% of its body weight each day, capitalising on whatever is in abundance.

Spawning fish in the winter are relatively easy prey in small upstream pools. Frogs and frog spawn in ditches, bogs and ponds make a feast in early spring, perfect for the arrival of cubs. Sea sticklebacks are plentiful in the autumn.

Otters are opportunistic hunters and when needs must are quite partial to the odd duck and even a low hanging bat!

Another thing they need is a decent place to live, especially if they are going to mate and rear a family. An otter home is called a holt and the ideal spot is under the roots of old riverbank trees. But man has tidied away many of these to improve the flow of rivers and reduce the risk of floods.

Meirionnydd Oakwoods is doing great work to revitalise our native oakwoods through clearing conifers and allowing new oaks to seed and other plant life to flourish. They're also giving otters a helping hand and recently ran an otter holt building course in Coed y Brenin.

Sixteen enthusiastic students lugged logs, hammered in stakes and insulated the twin-room holt with lots of branches tied down with wire to prevent it all being washed away by floods.

Why two rooms? So that Mum can get away from the kids. Why two entrances? To avoid confrontation if an inquisitive dog enters. Why a river view? That's what otters like - preferably a long way from roads where the car is their only predator.

Most students like myself were complete novices but some had previous form. One had built 23 holts already and was just seeking to refine her design and technique. Our instructor said it was as simple as assembling an Ikea flatpack!

Hopefully our riverside holt will be snapped up by a first time buyer ready for breeding next spring.

Otters and jasmine tea.