The Health Board (Terviseamet) is warning people to be careful on beaches in Randvere, Rohuneeme and Leppneeme beaches on the Viimsi peninsula due to the reported presence of cyanobacteria, also known as blue-green algae (Sinivetikad).
The agency recommends people monitor the condition of the water when going to the beach.
"If you notice that the water has turned a yellowish-green due to visible flakes and the entire shoreline is covered with a dense green mass with the smell of mildew, it could be blue-green algae," the Health Board wrote on social media.
Cyanobacteria are poisonous and can cause animals, children and the elderly to fall sick. Anyone who swims in water which contains the bacteria should wash the seawater off of themselves as soon as possible.
Symptoms of cyanobacterial poisoning may be similar to those of regular flu, including redness of the skin and eyes, tiredness, diarrhea, fever, runny nose and cough, muscle aches, tingling and cracking of the lips.
Editor: Helen Wright