For 50 years, Maracana has been the biggest football stadium in the world and the mecca of Brazilian soccer. But its iron structure is rotting because thousands of fans are relieving themselves on the terraces. Not wanting to miss even a second of a match by using the toilets, the Brazilians have long held to a tradition of urinating in the stadium's access ramps.

After years of this, the entrances' concrete and steel structures are now rotting. Engineer Luis Eduardo Cardoso said: "Our studies show there is corrosion in all the entrance points to the stadium and not in the benches area. We believe the main cause of this structural damage is people going to toilet.

"All those gallons of urine contain a lot of ammonia, which acts with amazing speed. It eats through the concrete and then acts like acid on the steel girders, which is why the corrosion is so devastating."

So seriously are the authorities taking this threat to the historic stadium that next week they are launching an "anti-urine" patrol.

The eight-man squad will patrol the corridors of the stands - which at capacity can fit 220,000 - and forcibly guide the fans towards the toilets.

"When there are big games it can get pretty disgusting here with a really horrible smell," said Cardoso.

"There is a huge volume of this liquid and it flows all over the ground. If we don't do something about it now, the very structure of Maracana could be destroyed."

The stadium officials are also renovating the toilet block. They plan to have 60 new toilets next to the bar, along with more facilities at every entrance. Francis Carvalho, president of Rio de Janeiro's sports authority, said: "The supporters wait until half-time before going to the toilet so as not to miss a minute of the match. "People can't be bothered to use the toilets because Brazilians learn to relieve themselves anywhere from a very young age."

Another problem, according to Carvalho, is that to date the stadium's management has been reluctant to invest in comfortable bathroom facilities.

"The fans have a tradition of getting really mad and smashing everything in sight if their team loses," he said. "They go to the bathrooms and rip toilets from the wall and break all the pipes, so we haven't really wanted to make the bathrooms any more enticing for them."

As well as renovating the toilet block, Maracana's engineers are replacing the damaged concrete and steel girders. Starting with the most corroded ramps, the engineers plan to erect new steel pillars, which will later be covered in concrete.

Sydney Pessoa, the co-ordinator of the renovation work, said: "I hope we will be able to encourage people to use the bathrooms. But with so many fans in the stadium it is going to be difficult providing facilities for everyone."

Maracana was built in 1950 to host the World Cup, the only time the championship has been held in Brazil. Pele, the legendary Brazilian footballer, described the stadium as having a "sentimental place in the heart of every Brazilian" and as being an "indispensable feature of our all lives".