Marlborough District Council has issued a list of 960 potentially polluted sites in the region.
Councils around New Zealand have been releasing similar lists following a ruling by the Ombudsman that such information should be made public.
Three sites are contaminated, including the former Carey's boatyard in Picton which is now part of a foreshore redevelopment.
The council says it is checking for any impact of former anti-fouling paints in the harbour.
It says the other contaminated sites are a timber treatment business in Conders Bend and a residence in Blenehim where paint was stored.