Outside, the temperature is hovering around zero. On a bleak, grey morning, Chester Zoo's car park is empty except for a little boy in a padded red anorak whose mother is trying desperately to fasten his zipper while he wriggles, eager to run.

Inside, basking in the airstream of an industrial-sized heater and pampered by an around-the-clock team of keepers is Karha, the reason for the boy's impatience. The baby Asiatic elephant, six weeks old and 21 stone, is already prancing before a small but rapt audience. She has only been on public view for a week and those who have had to be content with following her progress on a special zoo telephone line are thrilled to see her, at last, in the flesh.

"Ah, she's so sweet, so gorgeous," coos a woman at the front, as if peering into the pram of a powdered newborn child. Karha's mother, Thi-Hi-Way, a former circus performer, is outside in the freezing enclosure with the other adult elephants. She has rejected her offspring. Hence the scattering of keepers' duvets among Karha's straw. Every night someone sleeps with Karha, bottle-feeding her every two hours.

To many of her visitors Karha is simply a small-trunked cutesie. But to Chester Zoo, the largest urban zoo in Europe and a world leader in the captive breeding of rare and threatened species, she is a conservation triumph, the culmination of years of labour and investment. She is only the second Asiatic elephant to have survived the critical first four weeks in a British zoo. She is also a commercial godsend, already responsible for tripling the number of visitors to the zoo, the bulk of whose income comes from the money taken on the gate.

Despite the joy over Karha, Chester Zoo officials are more preoccupied this week with another new arrival, and a potentially predatory one - the entrepreneur businessman Phil Crane, whose company Deep Sea World is planning to build a huge aquarium at Ellesmere Port, just five miles from the zoo's front gate.

DSW already boasts the country's largest aquarium. It opened three years ago in North Queensferry, Fife, and is already one of the country's leading tourist attractions. When the weather is bad, families head for the great indoors. There, visitors wander through a 112-metre underwater glass tunnel while sharks, stingrays and hundred of other marine species swim past, inches away. The proposed Ellesmere Port aquarium will be twice as large as Fife's and Chester Zoo warns that it will dramatically cut its own visitor numbers, threatening breeding programmes such as Karha's and leaving the zoo itself to face extinction.

For its part, Ellesmere Port and Neston Council insists that the entire future of the struggling town - always regarded as Chester's poorer, grubbier cousin - utterly depends upon the proposed giant pounds 11m fish tank.

In his spacious office, heaving with learned books on wildlife, Dr Gordon McGregor Reid, director of Chester Zoo, talks scathingly of the aquarium. The setting is a world away from the girls in wetsuits who recently gathered signatures for a pro-aquarium petition outside Ellesmere Port's local supermarket. Strategies may differ, but politeness on all sides has all but broken down. Even the insults are aquatic: dealing with the smooth Mr Crane, who made a fortune in video rental before turning his entrepreneurial sights to the deep, is, says Mr Reid, "like trying to nail a jellyfish to a rock".

Mr Reid insists Mr Crane is deliberately setting up shop next door to his zoo so that he can poach its 800,000 annual visitors. What incenses him most is the pounds 3.1m European Commission grant for which Mr Crane has applied, with council backing, to help him do it. Chester and its zoo do not qualify for the development funds available to its more needy neighbour and Mr Reid complains it is "unfair" that such a large sum of "public money" could be used by a private company to put a charitable trust out of business.

Since the zoo registered its opposition with the local EC funding office six months ago, plans for the aquarium - then tipped to be within days of grant approval - have been on hold. There have been a flurry of independent assessments and reports. A decision on the grant will finally be made next month.

Suggestions from Ellesmere council, Mr Crane and local businessmen that the zoo "get into bed" with the private aquarium to create a tourist "dream ticket" adds insult to prophesied fatal injury. "The aquarium shows no interest in conservation," insists Mr Reid, coincidentally one of the world's leading aquarists, who insists he cannot ignore the ideological gulf between a highly respected, non-profit-making organisation dedicated to worldwide conservation and a fledgling private company primarily focused on profit and public entertainment. But he is clearly feeling the squeeze.

Meanwhile, Phil Crane, the zoo's bete noire, waits with impatience for next month's decision. A self-made Yorkshire man with forthright views, he argues the zoo has only itself to blame for its predicament. "I think the zoo wants to build its own aquarium and tropical rainforest, but they have been caught napping," he says. According to Mr Crane, the alleged lethargy is widespread. "Every tourist attraction in the area, including the zoo, is declining. I've told them, you can either sit there and watch or get off your backsides and market the hell out of Cheshire."

He argues the zoo has failed to develop as a showpiece for visitors and to capitalise on one of the country's greatest tourist areas, which also boasts one of the highest levels of local consumer spending. He puts the zoo's opposition down to "sour grapes" that someone should presume to do what it has failed to - and snobbishness that anyone from outside its cosy academic world should encroach on its territory.

He says that while he has no marine expertise, he has bought it in and denies that his aquariums are research- and conservation-free zones. "Yes, I make aquariums entertaining, but that doesn't preclude research or education," he argues. Like museums and academic institutions, Chester Zoo, he says menacingly, has been too long on a pedestal.

Mr Reid is aggrieved. "It's a bit like the boy in the playground saying join my gang or I'll punch your nose. Why should the zoo lend its reputation to an organisation with no track record and fewer visitors? If we operated like the aquarium, we would have three, not nine, elephants and only four chimpanzees, not 37. The public would be satisfied, but the zoo could not run a breeding programme. Our proud boast is that the animals are our only shareholders."

At Labour-controlled Ellesmere council, however, they are primarily concerned with the survival and well-being of the human population. And it has been a tough 10 years for Ellesmere Port's Homo sapiens.

The town has always had an identity problem, being an outpost of industrialism more suited to Merseyside than the posher, rural Cheshire to which it is so oddly attached. It grew up as a stop on the Shropshire Union and Manchester Ship Canals, but its heyday as a port is long past and its major manufacturing companies, Vauxhall and the Stanlow Oil Refinery, have cut their workforces substantially.

Stephen Ewbank, the council's chief executive, says Ellesmere Port faced a stark choice a decade ago - to die or reinvent itself. It chose to turn its face east towards its odd relation, and thus an economic strategy centred on tourism and recreation was born. "There were those who laughed at the notion of Ellesmere Port as a tourist or leisure centre," Mr Ewbank remembers. And despite what he says, many still do. But the town has undoubtedly succeeded in finding private-sector partners to help it to make something of its vision. The rundown dockside was redeveloped - complete with a new Holiday Inn - and Cheshire Oaks, a large recreation and shopping development on the outskirts of town, was created.

It is at Cheshire Oaks, at a junction of the M56 and M53, that Deep Sea World plans to set up shop. Once again, Ellesmere Port's strategic transport position may be its salvation. An American-style retail outlet village is already established and attracts three million visitors a year, though the words "Ellesmere Port" are curiously absent from the outlet's publicity. "The future of the borough depends on getting it right at Cheshire Oaks," says Mr Ewbank. "And we have several other multi-million pound developments resting on the Deep Sea World development."

Mr Ewbank is at first polite about the zoo's "misguided" concerns but quickly grows irritated with the "myths they naughtily perpetrate". Persuaded by Mr Crane's philosophy of "growing the cake" - raising the overall number of visitors to a region by increasing the attractions you have to offer - he insists the zoo will not lose out and might even gain. Edinburgh Zoo, he argues, did not suffer when the first Deep Sea World was set up just 14 miles from its front door and more visitors were lured to Fife.

Edinburgh Zoo, however, which has had its own difficult relations with Mr Crane, says overall numbers were affected in the short term and despite recovering believes that visitors from the local area are still down. A spokeswoman adds that it has yet to develop joint programmes with the aquarium because DSW has yet to show any conservation interest.

But Mr Ewbank complains that Chester Zoo is ignoring economic realities, both its own and the local region's."Charitable trusts are big businesses," he says. "If they don't realise that and face up to the real world, they are going to decline. The zoo is far too inward-looking."

That's a view heard often in town, and it suggests the zoo is right to fear that locals will be dazzled with the spectacle of the aquarium and seduced by the promised 90 jobs and spin-off employment.

Despite acres of space in the local press about the row, the zoo and the aquarium are essentially viewed as the same kind of organisation. Everyone in Chester knows about Karha, but most have little understanding of the zoo's wider conservation work. The zoo's own small aquarium, while nationally acclaimed, is no visual match for an 80,000sq ft tank on three levels which will boast one of the longest underwater tunnels in the world. And while the zoo's work with 25 endangered marine species is hugely important, the recent breeding of two-centimetre long African cichlids, nearly extinct in the wild, is hardly a spectacle to draw crowds.

Mr Reid says size should not matter, but it clearly does.

"Have you seen the zoo's own aquarium?" says one local man. "It's tiny and there's not much to see. The new aquarium is great for kids and great for the town."

Packing them in at the aquariums

Chester Zoo is the 17th most popular visitor attraction in the country (773,554 visitors in 1994), five places behind London Zoo (1.05 million) and 11 places behind Chessington World of Adventures (1.6 million), the zoo that has embraced the concept of the mass market modern theme park with most enthusiasm.

But a glance at the most popular tourist attractions opened between 1990 and 1994 reveals the rise of the modern British aquarium, with its spectacular glass tunnels and touch pools, a world away from the rows of small boring fish tanks that characterised its predecessors. Ten of the 20 top new attractions are aquariums, nine of which were opened by Sea Life Centres, a company started in Oban in 1979 and now run by Vandon Attractions.

Top 10 new attractions (1994 visitors)

Sea Life Centre, Blackpool 545,031

Cadbury World, Bournville 495,165

Deep Sea World, North Queensferry 436,232

Buckingham Palace (open for eight weeks) 420,000

Eureka! the Museum for Children, Halifax 414,000

Pleasure Island, Liverpool 365,000

East Point Pavilion, Lowestoft 348,556

"Anything to Declare?", Liverpool 312,000

Sea Life Centre, Brighton 272,000

Sea Life Centre, Scarborough 237,104