More than 187,000 plants and 19 tonnes of buds were seized between June and October in the region of Catalonia.
Spanish police have seized more than 50 tonnes of marijuana, the largest amount of the drug ever confiscated in the country.
Eight farms have been dismantled in the northeastern region of Catalonia and 20 people were detained on suspected electricity fraud and offences against public health, police said in a statement on Friday.
All the farms were dissimulated as supposedly legal hemp plantations and registered as owned by a trading company and located among other warehouses with legal industrial activity.
In total, agents seized 52 tonnes of marijuana, with more than 187,000 plants and 19 tonnes of buds between June and October.
In a separate bust earlier this month, Spain announced it had seized 32 tonnes of marijuana, which set a record at the time.
In June, the Spanish Tax Agency said, in reference to a different drugs operation, that cannabis was worth “between 2,300 euros ($2,290) and 2,500 euros ($2,592) per kilogramme”.
At that rate, 50 tonnes could have an estimated total worth could reach 125 million euros (nearly $130m).