An enormous algae bloom ­– 50 miles long – has been discovered in the English Channel. The swarm of skeletonema has come to the surface between the Lizard in Cornwall and Salcombe in Devon because of the warm weather.

Scientists at the Plymouth Marine Laboratory (PML) discovered the bloom and another off the south east coast of Ireland using satellite images.

They say that it poses no threat to humans and has appeared earlier in the year than usual thanks to the mild temperatures of the last few weeks. It would be visible from boats as a green/brown layer on the surface of the water.

Peter Miller, PML’s Earth observation scientist, said: “Skeletonema is a beautiful microscopic plant that, given the right conditions, reproduces rapidly to cover large areas of coastal seas.

“Over the winter nutrients have built up in the sea and the windy weather we have experienced recently has stirred them up to the surface.

“Combined with the now calmer conditions and bright sunny days everything slotted into place to enable this plant to reproduce and form a large bloom.”

Claire Widdicombe, a plankton ecologist also at PML, identified the plant from samples collected from the Channel near Plymouth, Devon, confirming suspicions that the bloom was not harmful.

“What is interesting is the timing of the bloom”, she said. “We would normally expect the spring bloom to be a few weeks later than this, although there is some variation and it all depends on being in the right place at the right time.”

The algae was discovered by scientists working on the AquaMar project, which uses images from space as an early warning system to detect algal blooms that might pose a risk to humans and the fishing industry.