There is still some debate over the make up of a brown slick which polluted the seas off St Agnes at the weekend.

Initially it was claimed that raw sewage was being pumped into the sea at Trevaunce Cove after a video of the slick was posted on social media.

But yesterday the MP for the area Cherlyn Mackrory told the Packet that testing by Defra and endorsed by the Environment Agency had found that the brown sludge contained mud and was run-off from fields above the cliffs.

She told the Packet: "I am glad it was not sewage, but any pollution/spills in our sea is unacceptable.

"I will continue to discuss this incident with South West Water, the Environment Agency and Government Ministers."

However many local residents and surfers were insistent that sewage was contained in the spill, with one describing it as the worst they'd ever seen as brown water was filmed pouring out of the overflow pipe onto the beach.

The surfer who filmed the slick told South West News: "Sadly the events in the video are on the increase, happening more often with less rainfall, rather than reducing.

"As a regular water user I can testify to this. It did improve in the late 90's / early 2000s after pressure from organisations such Surfers Against Sewage.

"But it has been on the increase again over the last five to ten years.

"Sadly, this is becoming an increasingly common occurrence, not just here, but all around the country's coastline and rivers."

In a series of Tweets South West Water said it was aware of the video and wanted to update people on what was happening.

It said its storm overflow at St Agnes was triggered briefly on Sunday following heavy rain.

"This was a short duration spill and is unlikely to have caused the level of discolouration shown in the video," they said 

"On this occasion, we believe there were other factors which contributed to the discolouration, such as mud in the water dislodged by the heavy rain flowing into the area from a nearby stream and runoff from agricultural land.

"We understand that this may be what you expect sewage to look like, but this is not always the case. We continue to increase investment in the region’s infrastructure as part of our ongoing commitment to protecting and enhancing the natural environment."

Meanwhile Jayne Kirkham, Labour's Parliamentary candidate for Truro and Falmouth, said she will be meeting with South West Water this week to discuss the crisis in sewage outflows onto Cornish beaches and into rivers. 

She said: "For the sake of our health, our ecosystems, and our economy, we need to stop this appalling practice of discharging sewage." 

She added: "In the River Fal, on beaches from St Agnes to Gyllyngvase, sewage is being pumped out into our waters day after day and we are - literally - sickened by it."

She said cuts to the Environment Agency's budget had left it unable to monitor spills as it should.

"Many overflows, like the one at the Prince of Wales pier or Pendennis Point, [in Falmouth] are not even monitored. The Conservatives have presided over a doubling of water companies dumping sewage in our waters," she said.