The lido shuffle: the clean, tepid water of Gourock's lido, one of the few remaining in Scotland, attracts old and young bathers in great number

It is so hot and still that the bunting that lines the street-side buildings of Gourock's outdoor swimming pool can hardly be bothered to flutter. It flickers languidly above the boxy white buildings.

The baths themselves are down the stairs, on the edge of the river. There the bunting has a little more vigour but the breeze off the Clyde, often eye-stingingly sharp, is merely refreshing. This can foster a false sense of sunscreen security. Stuart Boyle, the pool manager, lists among his many duties waking up patrons who are turning a dangerous shade of pink.

I have chosen the perfect moment to visit one of Scotland's last remaining lidos. The temperature is a delicious 21degrees and the water is a comforting 28 degrees. It is a week day and the district's children, who can swim free in all of Inverclyde's pools, are busy with their lessons, giving me peace to hammer up and down the lanes, splash about in the shallow end or just float peacefully in the filtered sea- water.

I could dive off the high board, if only I knew how. Afterwards I have my pick of sun-loungers and picnic tables on the large patio area. Were I on holiday in Spain, I would marvel at my good fortune. Instead I am an hour's drive from Glasgow.

The pool, 101 years old and showing its age, has been open since 7.30am. Boyle arrives at 7.15 to find a queue of silver-haired regulars, sturdy costumes and perm-preserving swimming caps rolled into their towels. Inverclyde's pensioners also enjoy free entry to the pool. Many travel there by bus, also free, bring their own sandwiches and spend the best part of the day gossiping their way through multiple lengths, a picnic and a newspaper in the sunshine.

This is Betty Irvine's fourth visit of the week. By 11.30 she has swum, showered, dressed and is sunning herself on a wooden bench, donated to the pool in memory of a past Provost, sipping coffee from a beige vending machine cup. It has foamy scum on top - catering is one not of the Gourock pool's strong points. "I always come on Monday, Wednesday and Friday and quite often the days in between as well. I know everyone."

At 77, she looks ten years younger and is by no means the oldest of the regulars. One friend only stopped coming in her 90s, when her eyesight failed. Irvine might, she says lightly, do 100 lengths of the 33m pool. She doesn't keep track. "If you start counting and someone talks to you, you forget. But I stay in an hour, sometimes longer."

Betty heads off, to the hairdresser. The sun is burning through the milky clouds.A Caledonian MacBrayne ferry heads out across the Clyde to Dunoon. One of the lifeguards sweeps the concrete floor with a stiff-bristled brush. Radio One burbles in the background, over the rhythmic splish and slap of length swimming and idle discussion of grandchildren's graduation ceremonies and two-for-one offers at the nearby monolithic branch of Tesco.

Stuart Boyle surveys his estate, the recently cleaned baby pool, the patio area which is yet to fill up with sunseekers. Empty, is looks vast and calm. But in the May-September season, more than 30,000 people come through the doors. During the school holidays it is an ant farm in Asda swimwear. Every millimetre of concrete has a child playing on it, each blade of grass is covered with a towel. He spends a lot of time convincing his dripping customers that there are no more sun loungers hidden in the store room.

Boyle remembers coming to the baths as a child, standing on the roof of the changing rooms and looking down at the swimmers below. That part of the building is now cordoned off and condemned, as is the main entrance on Albert Road and the tuck shop. He worked the poolside as lifeguard 14 years ago. Now he is manager and about to start on a 2 million refit of the Edwardian facilities.

Being the boss, he is also in charge of monitoring the weather forecast, breaking the bad news to four-year-old Scott that there are no Fab ice-lollies (he placates him with a raspberry Mr Men) and dealing with an unacceptably lumpy cup of soup from the hot drinks machine. He could also, if called upon, leap into the pool and save anyone who had got into difficulties.

He clearly adores the place but refurbishment is, he says, overdue. Built in the year Edward VII ascended the throne, today it's a classic council mishmash of boarded up historic features, sun-faded promotional banners and tagged-on afterthoughts. It was first modernised in 1935. In 1969, the water was heated for the first time. Today there is a tiny fitness centre for those who prefer to exercise with their clothes on but, despite overlooking the pool, with the hills of Argyll in the distance and the yachts, ferries and liners of the Clyde zipping past, there are no windows. The optimistically-named "changing village" has puddles on the floor, 1970s lockers and one long shower, shared by infants and oldies of both sexes. Despite being a magnet for families and children, there are only four large cubicles.

Tomorrow evening, the pool closes for the season. Come Tuesday, work starts to double the capacity of the gym and give it car showroom windows. There will be smart new changing rooms, a proper entrance and disabled facilities, including a lift from Albert Road. The design is clean and minimal; Boyle is resigned to consigning the pool's remaining Edwardian flourishes to the skip.

Ann Matthews always brings her own foodstuff."I plan," she says, "to spend the whole day here, getting a tan, reading my book and eating chocolate. Would you like a piece?"

Matthews, who lives further down the coast in Wemyss Bay, gets the bus to the Gourock pool every day of its 18 week season. She often hands in cakes or pizzas to keep the staff going. Now aged 63, she has been coming to the baths since she was a little girl. Her family lived just 10 minutes away.

"I remember when it was 10 shillings for a season ticket. During the school holidays we would be here three times a day. It was unheated in those days, the pool used to have stones, shingle, jellyfish in it. One day it was full of eels. At high tide, the water came into the changing rooms and sloshed around.

"We would go home for our lunch then come back afterwards. If it was raining, we would march there with our swimming hats on and our towels round our shoulders. Then we would be back for the afternoon. And we always had a chittery bite: a bag of crisps from the tuck shop. The ones with the salt in a little blue bag. They cost thruppence."

As the poolside day goes on, the average age drops. An eight-week-old baby, Emily, arrives for her first swim, with mother, grandmother and grandfather in attendance. She enjoys her brief dip but is not so keen on the changing process afterwards. Sharon Kennedy, 36, in a flirty red bikini that shows off her cherry tattoo, leaps in with four-year-old daughter Ellie. Two lads with bare chests strut in for a lunch-time session. Between 12 and 2pm, office workers plough up and down the lanes.

Gerry Malone, 52, comes every mid-day for a quick 50 lengths. Same again in the evening. Over the week he will cover around 25km.

"What makes it special," he says, screwing up his eyes in the midday sun, "is the unique location and that it's a 33m pool. It's heated, filtered sea water that's so clean that you can see from the shallow end to the deep end. I was swimming off Barra in the summer and my first thought was that it was so similar to the Gourock pool. Apart from the temperature of course.

"Because it's outdoors, you feel as if you have had an occasion, coming for a swim here. The regulars get to know everyone and the ad hoc visitors are a bit surprised to find this on Glasgow's doorstep. The sea breeze means it is always fresh."

Emma and Martin Peters are lying on the grass verge overlooking the patio, eating oranges, toasting themselves. They have driven down from Glasgow. Growing up in Colintrive, in Argyll, Emma looked across the Clyde at the lido for all her childhood. Today is her first visit. She is 37. "I have always known about this place," she says sheepishly. "I cannot believe I have never actually been before."