Prince Phillip was reportedly against construction of the £1.2bn 5.5km long six lane Shenzhen Western Corridor (SWC).
The road bridge spans Deep Bay between Ngau Hom Shek in Hong Kong and Shekou in China.
As president of the International World Wildlife Fund, he was concerned that birdlife in the Mai Po marshland area which lines Deep Bay would be scared off by the new crossing.
'The WWF was worried that the new bridge and associated works would reduce the birds' feeding ground - especially for the blackfaced spoonbill. There are less than 800 in the world, with 20% of them near Mai Po, ' says Arup project director Alex Kong.
But increasing cross border tourist and trade traffic has saturated existing roads between the two regions, necessitating the fourth crossing. The Shenzhen city government in China and Hong Kong highways department decided against the environmentalists' suggestion of a tunnel instead of a bridge on the grounds of cost. The SWC crossing links with the viaducts of another new highway - Deep Bay Link - so the tunnel approach to the 60m high viaduct at Ngau Hom Shek would have been too steep. Construction of the SWC began in August 2003 and will continue until December 2005.
Deep Bay is a misnomer, since it is actually just 3m deep for the most part, attracting birds hungry for fish in the mudflats.
Since the bridge will cross the Hong Kong/China political boundary, 3.5km of the structure will be built under Hong Kong environmental legislation and 2km under China's.
This has meant that work for each half has progressed completely separately - the Hong Kong side requiring a temporary access bridge to be built under the proposed structure to ensure that machinery does not travel across the mudflats. Arup is the consultant for the Hong Kong section of the SWC and connecting viaducts.
'We had to dredge silted up Gei Wais [fish ponds] and reinstate fish to attract more birds. We also have to vacuum the access bridge twice a week to prevent dust and debris falling into the bay, ' says Kong.
Oyster farms were relocated to ensure they were unaffected by the project.
The SWC crossing includes two 210m long navigation channels marked out by twin cable stay spans of steel construction and two 160m tall concrete leaning towers. Two thirds of the tower on the Hong Kong side has been constructed using jump form shutters and the steel deck for the cable stayed portion is nearing completion.
'The towers either side of the regional boundaries lean towards each other - a sign of co-operation, ' says Kong.
Approach viaducts consist of precast concrete spans with piers every 75m. Segments are 15m long and erected using balanced cantilever construction. The final three spans are due to be completed this September.
The SWC connects the 5.4km long Deep Bay Link (DBL) road with the proposed Route 10 at Lam Tei in Hong Kong.
But the £2.5bn six lane carriageway DBL has upset people living in rural villages along the route. Many villagers did not have land rights so the Hong Kong government was able to take over their properties, using police force if necessary.
'They sometimes made it difficult for us, ' recalls chief resident engineer Simon Tong.
'There are several ancestor graves near the route and the locals are concerned we'll disturb their peace; disturbing their Feng Shui. Sometimes machines were vandalised to stop us working, ' he says.
'In some cases we have to relocate tombs and in others we hold ceremonies for the peace of the dead people'.