The Hellenic Biodiversity Observatory released a list of beaches where jellyfish appear more frequently. The map data is derived from the special recording system that the Observatory has set up in order to record the and the jellyfish appearances are recorded.
The environmental organisation says the system automatically registers the location, so the cases of errors are kept to a minimum level.
These are the beaches for July:

Beach Drepano
Psatha, Corinthian Gulf
Vlachorema, South Eastern Pelion
Anavyssos beach
Alepochori Megara
Glyfada Beach
Antiparos
Praxilio, Kiato
Beach Diminio, Korinthia
Kamari, Old National Road of Corinth Patras
Sykia Xylokastro
Beach of Avdira Xanthi
Potamos beach, Epanomi
Katerini Beach
Porto Rafti, Ag. Marina
Katharonas beach, Nafplion
Kalamaki, Akanthos
Corfos Corinth
Zacharo Ilias Beach
Akrata beach
Asteras beach, Glyfada
Rovies beach
Kochili beach, North Euboea
Portes Beach, North Kynouria
Alykes Anavyssos Beach
Zorkos beach, Andros