It's blooming hot at last...and blooming colourful too.

This aerial picture of Ranworth Broad by Mike Page reveals one of nature's spectacular shows, believed to have been brought on by the welcome return of summer-like temperatures.

However, while the sudden bloom of blue-green algae looks attractive from a distance, broad owner Norfolk Wildlife Trust (NWT) has been quick to put up signs alerting visitors to the potential health hazards.

For reasons which are not fully understood, bloom and scum-forming blue-green algae are capable of producing toxins which have been known to kill wild animals, farm livestock and pets.

People coming into contact with affected water can end up with skin rashes and suffer other symptoms including stomach upsets and eye irritation.

While Ranworth Broad is closed to hire boats, reducing the potential exposure to humans, the bloom can also be seen on parts of neighbouring Malthouse Broad, leading to busy Ranworth staithe which is popular with Broads holidaymakers.

Blue-green algal blooms have also been spotted over the past few days on other parts of the Norfolk and Suffolk waterways, including Barton and Hickling broads.

NWT spokesman Ed Parnell said the phenomenon, caused by the sudden, accelerated growth of algae, occurred most years and was down to weather conditions.

He said: 'It is more striking from this aerial shot; our visitor centre manager did not notice it to begin with.

'Blooms may be more common at spots like Ranworth because of the still, wildlife-rich water which is unaffected by boats apart from our own pleasure boat.'

He said they had put up signs to alert visitors, advising them not to put their hands in the water during boat trips; a notice would also be put up in the NWT-run tourist information centre at the staithe.

He said: 'The bloom is not affecting our operation at all and access to our visitor centre at Ranworth is normal.'

A spokesman for the Environment Agency said they had been contacted by the Broads Authority last week and carried out tests at Barton Broad which confirmed a blue-green algal bloom there.

She said: 'We do not advise managers of waters what to do if it is confirmed as blue-green algae but inform them of what the effects of the algae can be on wildlife and people and it is up to the managers what they choose to do.

Andrea Kelly, senior ecologist at the Broads Authority, said: 'Our protocol is that if we own the site we would put up notices and possibly get the water tested by the Environment Agency.

'We also work in partnership with and offer guidance to other lake owners, for example NWT which owns Hickling and Barton broads.

She said the bloom might last several days until it was dispersed by a rain shower or a change in weather conditions.

'It is more likely to occur at a site like Ranworth Broad which is not connected to the river and where the water just sits,' she said.

She said that in bad cases, fish deaths could occur.

Ms Kelly said: 'People on boats can help by using environmentally-friendly products in the shower or when washing up. The public can also help by using less water at this time of the year to preserve levels in the rivers and lakes.'

Mr Page, a regular flyer over the Broads, said the bloom at Ranworth was the worst he had seen in at least a decade.