Boats, cars, properties and 500 thousand dollars worth of cash

Those are just some of the 3.5 million dollars worth of assets police have seized after busting a a nationwide drug dealing business.

Operation Chestnut is a 10 month investigation into the sale and supply of methamphetamine in Tasman, Wellington, Central and Eastern Police districts.

It's seen police execute 18 search warrants and arrest seven people.

This includes a 44 year old man - alleged to be the main offender.

He's charged with 12 offences including money laundering and conspiring to deal methamphetamine.

Detective Inspector Paul Baskett says this type of offending undermines the wellbeing of our communities creating significant social harm.