Many of the UK's top tourist attractions have suffered a slump in visitors due to poor summer weather and the London Olympics.
Some attractions in the capital saw numbers drop by 60% during the two-week period of the Games.
Visits to outdoor-based sites were the worst hit by "appalling weather," according to the Association of Leading Visitor Attractions.
London Zoo, the Tower of London and Kew Gardens were among the attractions that suffered a drop in numbers over the summer.
Visitor numbers also fell throughout England and in Scotland.
Visitors to garden and leisure sites in London were down by 21% over the summer, according to Alva.
About 20% fewer tourists visited the heritage and cathedral sector and the capital's museum and galleries attracted 13% fewer people.
Alva chief executive Bernard Donoghue described the figures as "sobering reading".
He said: "The summer of 2012 has been a difficult time financially for our most popular and best-loved visitor attractions.
"For gardens and outdoor attractions across the UK, the appalling weather during much of the year has led to one of the worst trading periods since 2001 - the year of a foot-and-mouth disease outbreak."
Donoghue told the BBC: "For London attractions, the Olympic period was one of their worst trading periods in living memory and for visitor attractions, the summer is their equivalent of retailers' Christmas.
"Once lost, the business can't be won back".
He insisted that Alva viewed the Olympic period as a short-term loss for long-term gain.
"We are working with the local and national tourist boards and others to turn the millions of Olympic TV viewers who loved how Britain looked into visitors who will come here in the next months and years," he added.
Alva's 43 members manage nearly 2,000 tourist sites which attract more than 100 million domestic and overseas visitors each year.
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