BIG HAUL: Constable Mark Watson, of Reefton, with some of the annual West Coast cannabis bust.

Cannabis on the West Coast has flourished despite the drought-like conditions.

The region's annual police cannabis bust was due to finish today with about 3000 plants found from Karamea to Franz Josef by this morning.

Operation head Sergeant Russell Glue, of Hokitika, said today he was surprised the illegal crop was in such good condition considering the dry weather that had gripped the region.

DEIDRE MUSSEN/Fairfax NZ BUSTED: An Air Force Iroquois prepares to land at Kumara raceway with some of the cannabis stash police have found.

''I would say they probably have had to water the plants though.''

About 15 to 20 officers were involved in the six-day aerial eradication operation, along with 12 New Zealand Air Force personnel and an Iroquois helicopter.

Glue said the number of plants found was about 700 fewer than last year.

''Over the last eight or nine years, it has been trending down. We would like to think it's because of brilliant policing.''

However, he said the West Coast was still one of the country's key cannabis growing areas.

Most of the plants were found hidden in bush in rural areas.

Two people had been arrested and a third had been summonsed to appear in court. All faced cannabis cultivation and other drug-related charges.

Glue said removing cannabis from society was important because of the illegal drug's negative impacts.

All the plants had been destroyed.

The haul was worth more than $4 million for its impact on society, including hospital costs, crime and other social effects, he said.

Its street value could be up to $3m, with a mature processed cannabis plant worth about $1000, although the plants varied in size from seedlings up to fully-grown plants.