Blue-green alae form on fresh or brackish water (or discolour water without forming a floating scum). They look green and sometimes turn bluish when scums are dying.
What it causes: Some species of cyanobacteria are capable of producing neurotoxins.
Poisonous cyanobacterial blooms cannot be distinguished easily from non-poisonous organisms such as true algae, without examination by microscopy and testing for toxins or toxicity.
Send water samples containing bloom material to labs that specialize in this work – including state vet labs.
Note: Do not expose your bare skin to these blooms because irritation can occur. Use plastic gloves when obtaining samples.