It has become a big no-no in school lunchboxes because of its unhealthy reputation.

But it seems that Sunny D, formerly known as Sunny Delight, is not half as bad for children as it is for fish.

Around 8,000 litres of concentrate used to make the drink leaked into a watercourse on Wednesday morning, turning the river bright yellow.

Dozens of fish were found floating on the surface, poisoned by the lurid mixture.

The spill of 'sub-standard' juice was a category one pollution incident, the most serious kind, according to the Environment Agency.

It was caused by a split in an underground fibreglass tank at the Gerber Foods Soft Drink factory in Bridgwater, Somerset. Approximately six tons of juice and concentrate, due for disposal, seeped into a tributary of the River Parrett.

Gerber employees began a major mopping-up operation to stop the juice reaching the river and causing more environmental havoc.

Workers created a sandbag wall and dug trenches to stop it seeping any further.

As they toiled, three tankers were called in to pump as much of the spillage out of the watercourse as possible.

The damaged tank was emptied and pits around it were excavated to prevent juice that had already spilled travelling further.

The emergency action successfully stopped the concentrate reaching the river, according to Gerber personnel director Paul Hurst.

"We took swift action in preventing further seepage," he said.

"As far as I am aware, this is the first such incident."

More than 10 million litres of juice and soft drinks are produced every week at the plant.

Mr Hurst explained: "We take extreme care with the quality of our juice and if the concentrate or the finished product is not to our required quality standard, it is contained until being removed by tanker for sustainable disposal.

"Although orange juice is a natural substance, we obviously needed to deal quickly with its concentration in the watercourse.

"Gerber personnel were deployed and we worked closely with the Environment and Drainage Board to successfully bring the situation under control within a very short timescale."

Catherine Lockwood of the Environment Agency said: "The visual impact of this incident was immediately apparent.

"We will be carrying out a detailed investigation to assess the impact it has had on the surrounding waterways."

Asda supermarkets recently withdrew Sunny D from the shelves, citing a slump in sales.

The juice drink's name was changed and a marketing campaign launched after criticism from nutritionists, who claim it contains unhealthy levels of sugar and additives.