Dog owners have been warned to keep their pets away from the lake in Verulamium Park after several ducks were seen floating dead in the water.

One dog walker told the Review she had seen the bodies of 12 ducks caught up in the reeds last week and has avoided taking her pets to the lake since.

St Albans District Council, the RSPCA and the Animal and Plant Health Agency are investigating but as yet the cause of the duck deaths remains a mystery.

Dog walker Jess Down said she saw eight dead ducks caught in the reeds on Friday and another four when she came back on Monday.

She said: “It was by the bridge in the lake, where all the reeds are. I called the council who said they were aware but they didn’t know what it was.

“I asked them if the ducks were dying was it safe for the dogs to be drinking out of the water – but they just said if the dog drank out of the lake they would advise it gets taken to the vet immediately.”

Jess criticised the council for not doing more to warn dog walkers and park users of the potential danger posed by the water.

She continued: “They knew this problem was going on, but I didn’t see any warning signs. There is now a public notice in the Inn on the Park – but I don’t think that’s enough.

“I’m avoiding the lake now with the dogs.”

Animal care group Petrelief posted a warning on their website suggesting owners “do not let your dogs in the water there just in case”.

Speaking on behalf of the group, Lisa Cooper said one of her clients' dogs was taken ill after playing in the lake.

She said: “When one of my walkers saw the ducks, she called the council because she was concerned about the dogs – they were her first thought. There were no warning signs.

"One of my clients’ dog has been ill with diarrhoea since going in the lake; speaking to the owner the vet would be interested to know if it might be related to whatever is killing the ducks once the council investigation finishes.”

The council said they were waiting for test results and appropriate action would be taken when these had been received.

Richard Shwe, head of community services at St Albans District Council, said: “We are aware that some waterfowl on the lakes at Verulamium Park may have been affected by an unidentified condition or illness.

“We are working closely with the Animal and Plant Health Agency (APHA) and the RSPCA to monitor their health.

“Tests are being undertaken by APHA to find out what is causing more wildfowl deaths than we would normally expect at this time of year in the park.

“We are awaiting the results of these tests and will take appropriate action once we have received them.”

He continued: “We have placed signs around the lake to keep people informed. These also advise dog owners to keep their pets out of the water as a precaution.”