Tests carried out by the Environment Agency have shown early signs of toxic blue-green algae returning to the pond.

The deadly strain killed about 5,000 fish when it appeared last year, and the town council is bracing itself for the return of the virus.

Petersfield Town Council clerk Neil Hitch said: "We had a letter from the Environment Agency confirming the presence of blue-green algae.

"It is not in dangerous quantities and not yet blooming, but it is still present.

"So it was an anticipated warning that it will happen at some stage throughout the summer.

"We had communications with the Environment Agency and with David Fitzgerald from the district council's environmental health department about how we go about informing the public.

"It was agreed for us to put up our warning posters and it was agreed to continue staging events on the pond, which we will keep under review throughout the summer."

Residents are being advised they should avoid contact with the water and prevent their dogs from going near it, and if they do to wash themselves immediately.

Despite this, the water was still declared safe for use at a rowing regatta held at the Lake on Sunday.

"We are trying as soon as we can to treat the water," Mr Hitch said.

"As for the future, the council is pretty much of the view that we need help.

"Really we are waiting for the Environment Agency to give us a lead.

"Councillors are well aware that they are not marine water experts, and the Environment Agency must have come across similar blooms in similar-sized stretches of water elsewhere.

"We are looking for guidance over the best way of solving the problem."

The town council has attempted to arrange an emergency meeting with the Environment Agency over the next fortnight.

It has also contacted specialist companies who claim they can get rid of the algae, but the town council is not keen on spending thousands of pounds of taxpayers money with no guarantee the outbreak is cured for good.

Environment Agency spokesman Joe Giacomelli said: "I can confirm that tests have shown that there is blue-green algae present in the pond but no algal blooms have yet appeared.

"They tend to flourish due to warm weather conditions.

"We will be doing further tests.

"In the meantime we advise people to keep their pets away from the area as a precaution."