Lake Bled looks too good to be true: a glassy expanse, broken only by a tiny island with a fairytale church spire, and fringed with thick green forests and hard, grey mountain peaks. At the lake's edge is the finishing touch: a medieval castle perched on a steep rocky pedestal.

In fact, it's so picture perfect that on approach you expect to bump up against a glass wall, like Jim Carrey in The Truman Show. But Bled - a melted glacier pooled between three alpine ridges in the northeast of Slovenia - really does exist.

And although it's not as well known as Como or Garda, it's hardly a secret: Bled has been a tourist centre since the enterprising Swiss doctor Arnold Rikli founded a "Natural Health Institute" here in 1855. Now, in the summer months, it gets 5,000 visitors a day.

I visited in early November, when the town downs tools between summer and winter seasons: a misty morning walk around the 6km perimeter was silent apart from the odd car; solitary apart from local joggers (one of whom breezed past me three times).

There are regular municipal litter collections and a keen local pensioner who patrols the perimeter every morning, so you can take in the oaks and lime trees and spot the dark shapes of fish free from unpleasant distractions. The lake is well-stocked: its 11 species - including lake trout and catfish - are maintained by Bled's fishing club, which has a five-year breeding plan and strict controls on catching.

Mallards and mute swans glide across the surface, and many species winter here, including kingfishers, grebes and cormorants, all watched over by the Slovenian bird observation society. The water, constantly monitored by government scientists, is as clean as it looks, and a pump-driven circulation system prevents eutrophication.

Bled is protected both nationally - by the ministry of the environment - and internationally, as it is in the "transition zone" around the UNESCO Biosphere Reserve of the Triglav National Park.

Building is tightly controlled in the town centre, and forbidden around the lake, where the handful of scattered villas have hardly been added to since the Second World War. Lake transport is provided by family-run pletnas (traditional wooden oar boats); in bad weather three electric boats take over.

Other motor boats, and most watersports, are not allowed. Swimming is confined to three areas, including, in summer, a lido (€6.50) that regularly wins awards for its cleanliness and facilities.

The town has a responsible approach to waste: glass, paper and plastic are recycled and most waste water is collected by a new sewage system, reducing the chance of it reaching the lake. Over the next few years all the outdoor lamps in Bled will be replaced with downward-pointing bulbs to reduce light pollution.

Generally, the locals benefit from Bled's tourism. Money from tourist taxes on hotels and income from the lido and other attractions funds maintenance works. Tourism provides employment, too, although many say that wages for local hospitality jobs are too low.

Food in Bled is generally sourced from within the country (and often the locality: I ate a delicious roasted trout farmed in nearby Bohinj). Slovenians are proud of their produce. When the castle restaurant tried to cut costs by selling Czech water, diners, appalled at being served a foreign drink in a national monument, were quick to complain, and the Slovenian spring water brand was reinstated.

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