FIVE years after the opening of the Eden project in Cornwall, the same team of architects, led by Sir Nicholas Grimshaw, have designed the world’s largest freshwater aquarium at a disused clay pit in Bedfordshire.

Its centrepiece will be two 1.5m gallon tanks, home to some of the most unusual fish, reptiles and amphibians on the planet. These will include rare breeds of crocodiles, turtles and snakes.

Glass tunnels will lead visitors through freshwater habitats from the Amazon rainforest, the African Rift Valley and the Mekong Delta, under a vast heated tropical “biome” the length of three football pitches and more than 130ft tall.

As well as being a conservation project, the £365m venture will include a water leisure park with rides and wave pools, to help it to achieve its target of 1.6m visitors a year.

The scientists behind the project hope to feature rare exhibits, such as the 15ft black caiman alligator, which is on the brink of extinction. The largest fish will include the giant bonytongue, under threat because of the demand for its huge scales in Japan. It can grow up to 9ft long.

Many other creatures will come from southeast Asia, where illegal snake harvesting for skins and meat has meant that more than 8,000 snakes a day are being killed.

The park is expected to feature reptiles on the critical list or nearing extinction, including the Panamanian golden frog, which could be extinct in five years without human intervention, and box turtles, also threatened due to hunting.

Collections from the River Amazon may include more common species such as the giant green anaconda snake, which can grow up to 30ft long, and the long mop headed lizard, which can run across water without breaking the surface. Poisonous frogs and flying snakes will live in the trees.

Of the 700 species to be housed in the aquarium, about two-thirds will be acquired from captive breeding programmes and a third collected from the wild. It will seek to release some species bred in captivity back into the wild.

Mark O’Shea, reptiles and amphibions adviser to the project, said: “This will not be some colonial expedition to pull out species from around the world. But if there is a chance that a rare species is located where someone might pick it up and take it away for a delicacy or for its skin, we will look to try to save it.”

He added: “Although there are no quarantine laws we will also need a number of permits to bring back any species. It will be a long process. It is not a stamp collection.”

Peter May, chairman of the consortium behind the project, the National Institute for Research into Aquatic Habitats (Nirah), said: “Many freshwater species and habitats are facing extinction and not enough is being done to highlight their plight. We want to try and change this through conservation and educating people.” Nirah has assembled a team of more than 100 experts to advise on the project.

Architects at Grimshaw will use the same technology as the biomes in the roof of the Eden Project, comprising air-inflated pillows made of a plastic material called copolomer. Jolyon Brewis, associate director of Grimshaw, said: “We learnt a lot through working on the Eden project about how to make very large enclosures in the lightest and most transparent way possible, because we need to get the best conditions for plants and, in this case, animals, to recreate as closely as we can the natural conditions.”

The project will dwarf existing aquariums in Britain. By comparison both the Blue Planet aquarium in Ellesmere and the National Marine Aquarium in Plymouth hold more than 800,000 gallons and the Deep, in Hull, has 550,000 gallons. Most existing aquariums in the UK are by the sea to enable them to pump in sea water and discharge it as waste. The Tennessee Aquarium in America holds 400,000 gallons of fresh water.

The Nirah project, to be built on a 250-acre site four miles south of Bedford, intends to add leisure attractions to boost its visitor numbers to 1.6m — approximately three times more than any existing aquarium.

The biome will house a hotel whose bedrooms will have private terraces with views across the aquatic collections. There will be a water leisure park with rides, wave pools, an outdoor beach and a scuba diving centre with a snorkelling pool.

There are plans for a research centre and science park to study different species in the hope of discovering drugs based on the toxins, venoms and secretions produced by the creatures.

Planning application will be made in the next few weeks, and it is hoped to open in 2011. Tim Malynn, environmental director of Bedfordshire county council, said: “We are very excited about the project.”

It has already received £6m of government money and Nirah hope to raise £50m through a lottery grant. May said he would raise £280m through an Alternative Investments Market listing in 2008, and a further £100m through debt finance.

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