Dog owners have been warned to take extra caution after "deadly" blue-green algae was spotted in Norfolk's waterways.

The Broads Authority has issued an alert following the discovery of the toxic substance on Thursday, July 28.

It was confirmed to be present at Barton Broad and South Walsham Broad in the county.

Bacteria in the algae poses a particular risk to dogs and it can prove fatal.

In a Facebook post, a spokesperson for the Broads Authority said: "Blue-green algae (Cyanobacteria) has recently been reported and verified to be present at South Walsham Broad and Barton Broad.

"Please ensure that you stay out of the water and keep children and dogs under control in the area.

"Remain vigilant for signs of blue-green algae in other locations across the Broads as it is highly likely that there will be additional blooms in the area.

"Blooms of blue green algae can threaten public health as well as the health of dogs, cattle, fish and other wildlife. It poses a particular risk to dogs and it can be fatal in some circumstances."

What is it?

According to dog health experts Kennel Club, dogs are most commonly exposed to the toxins by "swimming, playing in, or drinking from contaminated water".

Blooms can look like "pea soup" and be blue-green in colour, or can even be red, brown or black.

It can also smell "musty, earthy or grassy", and you may sometimes see foam along the shoreline.

The algae can be found throughout the year but periods of hot warm weather can increase the likelihood of it forming.

What are the symptoms of blue-green algae poisoning?

Effects can vary but range from dribbling, tiredness, vomiting and diarrhoea (both of which may be bloody) to effects on the heart and blood pressure, convulsions, problems breathing or organ failure, according to Kennel Club.

Symptoms can start within a few minutes or within an hour.

Many cases are life threatening and dogs can die very quickly.

What to do if your dog is poisoned

Dogs need rapid treatment so should be taken to the nearest vet as soon as possible.

The Kennel Club say getting treatment as fast as possible is key to improving their chances of survival.

People can report sightings of blue-green algae here: ceh.ac.uk/our-science/projects/bloomin-algae