Cruise ships that empty the water from their swimming pools when in the port of Palma have led to six contamination warnings since 2010, according to the Spanish government.
The last such warning was on July 8.
Solar cream used by bathers is the cause of the environmental fears, according to the government.
This latest incident comes as the Balearic government is under pressure to curb the number of giant cruise ships which are visiting the port of Palma.
More than 10,000 people signed a petition calling for a ban on the mega cruise ships earlier this month.