For the Test, which runs through the grounds of Broadlands, the Mountbatten estate in Hampshire which was his firstnight venue, is about to lose all its salmon.
The Test is better known for its trout, and is Britain's most glamorous and expensive trout river - local folklore insists that on his wedding night Prince Charles, chairman of the Salmon and Trout Association, fished the evening rise, when the trout are easiest to catch - but it has also had a significant run of salmon which in recent years has dwindled considerably.
Research by the Environment Agency claims that stocks have slumped from 4,000 fish in 1975 to 623 in 1996, and present runs are estimated to be 32 per cent of the minimum required for the stock to be self-sustainable.
"The fish are at conservation-critical levels and require immediate attention to assure their continued existence," said an Environment Agency spokesman. "Failure to act is likely to result in the extinction of the stock."
The reason for the crisis is that both the salmon and the trout using the river to lay their eggs need clean gravel, but in recent years, as the river's flow has decreased due to low rainfall and high abstraction, the silt has built up and concreted on the gravel's surface.
There are also problems with many parts of the river now being unsuitable for nursery stock, with poaching and general over-exploitation.
Last week the agency launched a 10-year, pounds 1.7m plan to save the salmon, the first of 62 such schemes on Britain's rivers, and appealed for financial help to carry it out as it cannot fund the scheme on its own.
Its solutions include blasting the gravel with high-power hoses, using Army-style intelligence to trap poachers and trying to persuade anglers to put back the fish they've just paid to catch.
The Test attracts celebrities from all over the world. One angler even flew in from Texas, marched into nearby Winchester Cathedral and demanded his tackle be blessed on the grave of angling guru Izaak Walton.
Former United States President Jimmy Carter, rock stars Eric Clapton and Roger Daltrey, and entertainers Bernard Cribbins and Max Bygraves are all regular visitors. Anglers pay up to pounds 185 a day just to catch a trout.
The agency is spending around pounds 160,00 a year on the river and the fishing owners themselves spend another pounds 200,000.Reuse content