More than €20,000 of the drug was found earlier today in a house in Lettermacaward.
An amount of cash was also discovered in the raid on the house.
Donegaldaily.com understands that equipment used in the cultivation of the drug was also found by Gardai who raided the house.
The 43 year old man who was arrested and is being quizzed is from the locality.
A total of 47 plants worth an estimated €18,800 and cannabis herb worth a further €2,500 was discovered.
A Garda source said “We have recovered a large consignment of cannabis and an amount of cash.
“Forensics officers are currently going through the property and the details found will form part of our investigation.
“This was an organised operation and a man is in custody as a result of the Garda investigation.”