Dog walkers are being warned to take care if strolling around the Argal Reservoir in Penryn after toxic algae has appeared on the lake.

Pet owner Sarah Mason took to Facebook early on Wednesday to warn others after her dog fell ill following a walk at the popular spot.

Sharing a picture of the spot, she wrote: "Sadly this toxic blue green algae is back at the Argal Reservoir.

"It is highly poisonous to dogs - I have just spent the night at the emergency vet with our young collie.

"Please share this warning - luckily Bean is ok but the toxin works within 15 mins and is normally fatal."

The reservoir is operated by the South West Lakes Trust, and wardens said they will be putting signs around the site to make sure owners keep dogs on leads and out of the water.

The trust will also work with local farmers to reduce runoff of harmful nutrients into the lakes.

Beth Heasman, West Cornwall countryside warden for the South West Lakes Trust, said: "I’m very sorry to hear about the dog and very glad that he was alright in the end.

"We were surprised to see that picture as myself and colleagues have been there the last few days it must have suddenly come up and the wind blown it into that bay.

"It is also an area where we are currently experiencing a lot of run off problems from the neighbouring land owner who has started to use that field for maize planting which is causing pollution problems for us as well as washing out the path."