A warning has been issued about potentially-toxic algae in a lake at Stevenage's Fairlands Valley Park.

Blue-green algae has been discovered in the main lake, which could cause a risk to health, according to Stevenage Borough Council.

"Not all blue-green algae are toxic. However, you can’t tell just by looking at them, so it’s best to assume they are," read a statement from the council. 

"Therefore, we ask that you stay away and not let you or your pet enter the water.

"If you or your pet have become unwell after contact with water that you think may be contaminated with blue-green algae, we’d strongly recommend that you seek immediate medical or veterinary advice."

Blue-green algae, technically known as cyanobacteria, is a collection of microscopic organisms that are naturally present in lakes and streams.

Under certain conditions, blue-green algae can become abundant in warm, shallow, undisturbed, nutrient-rich surface waters that receive a lot of sunlight.

Stevenage Borough Council has said it is "working closely with the Environment Agency" to monitor the issue, and that there have been "no observed impacts on the local wildlife and fish stock".

The algae is not treatable at this time, with warmer weather being blamed for its growth.

"The weather being warmer than usual at this time of year has contributed to the algae forming," the statement continued.

"We anticipate a significant reduction in blue-green algae levels as the colder winter conditions set in.

"It's not currently feasible to treat it, but throughout the year, we've successfully applied natural barley straw extract and dyes to the water treatment to keep algae and bacteria at bay without harming the fish stock and wildlife.

"Moreover, we have two large aerators that operate at night, effectively boosting the oxygen levels in the water for the fish."