Sampling undertaken by council this month indicated blue-green algae levels have increased to amber alert at Telarah Lagoon and remain at high alert for Walka Water Works

Blue-green algae are microscopic cells that grow naturally in Australian fresh and saline waters.

However, when conditions are favourable for algae growth, blooms can occur.

Blooms appear as a thick paint like accumulation on the water's surface or as small green floating dots. Scums are normally green or blue-green in colour and have a distinctive earthy smell.

Maitland City Council's planning and environment group manager Matthew Prendergast said the rise was cause by high temperatures and low flow rates in dams as well as still water bodies.

"The potential exists for algal blooms to appear in a very short time period and caution must be taken using and entering non-flowing waterbodies," he said.

"Once an algal bloom has developed, there isn't a great deal authorities can do to reverse the situation except wait for a climatic change. Council will monitor the lagoons at Walka Water Works, Telarah and Rathluba for blue-green algae growth over the summer months."

Blue-green algae can be a serious human health and environmental problem, with the release of toxins and skin irritants.

Domestic pets and livestock can also be impacted if they come into contact with water affected by an algal bloom. Blue-green algae may contain toxins, which cannot be removed through boiling the water.

Blue-green algae may cause severe stomach upsets, nausea and skin irritation in both people and animals. If people believe they or their animals have been affected by blue-green algae they should seek medical attention. To help reduce the likelihood of a bloom occurring in one of Maitland's water bodies this summer people can reduce the amount of nutrients going into local waterways by washing vehicles on the grass, removing leaves and grass clippings from gutters and by applying fertilisers as per packaging instructions.