Warning signs have gone up at a Northumberland nature reserve after two dogs fell ill.
The pets are believed to have drunk water from the pond at East Cramlington Local Nature Reserve.
The former colliery site is owned by Northumberland County Council.
Mike Jeffrey, council countryside and green spaces manager said: “We received reports that two dogs had become ill after ingesting water at East Cramlington Local Nature Reserve pond.
“We immediately erected warning notices around the water and at the entrance to the site to warn owners to keep their dogs out of the water.
“The Environment Agency has carried out tests on the pond water and confirmed that traces of blue green algae had been found in it.
“This algae occurs naturally in water bodies but can sometimes be toxic to humans and to animals.
“We appreciate how distressing this unforeseen incident has been for the dog owners involved.
“We have not had any previous reports of blue green algae in the pond at East Cramlington, and as algal blooms are more commonly associated with warm conditions it is particularly unusual to get an outbreak this early in the year.
“We are now taking action to tackle the algae by placing straw bales in the water to absorb the toxins, but dog owners are advised not to allow their dogs in the water. ”
The reserve has a pond dipping platform, a wheelchair/buggy friendly path through the site, free car parking facilities and a picnic area.
Swans breed on the pond each year and it is frequented by mallard ducks, coots and moorhens.
The site is of value to a range of declining lowland farm birds including skylark, song thrush, linnet, grey partridge and yellow hammer, and supports a wide range of butterflies.
East Cramlington Ponds, a Northumberland Wildlife Trust reserve and a Site of Nature Conservation Importance, lies immediately south-east of the Local Nature Reserve.
An Environment Agency spokesperson said: “We received information that one dog had died and two others suffered illness which required treatment by a vet.
“The dogs had reportedly been in a small pond at East Cramlington Nature Reserve.
“An Environment Agency officer attended the site.
“Discussion with the vet indicated that the signs and symptoms observed may be indicative of blue green algae poisoning.
“Samples have been taken from the pond and examined. We’ve so far found no evidence of a toxic algal bloom but we will continue to monitor the situation.
“As a precaution, we’ve asked the local authority to put advisory notices around the pond and nets containing barley straw into the pond itself. The chemicals released from the straw as it breaks down acts to inhibit the growth of blue green algae.”