Another Canterbury waterway has been contaminated by toxic algae

The Canterbury District Health Board has issued a public health warning for Lake Pegasus.

Medical officer of health Dr Cheryl Brunton says people and animals - particularly dogs - should avoid the area until the warning's been lifted.

She says the algae looks like dark brown or black mats - and exposure may cause rashes, nausea, stomach cramps and numbness.

Brunton says people should see their doctor right away if they show any symptoms.

There's also a warning in place for the Selwyn River near Glentunnel.