"Every time there is a new bit of earthworks, a new development takes place, unless that sediment is managed on site that sediment gets washed into the harbour, that attracts a lot of contamination."

Since the removal of forests 150 years ago and ongoing intensive land use, sediment has been going into the Gulf.

We look at how councils manage land development and some great new initiatives to help remove sediment with tree planting. We explore Auckland’s 100-year-old sewerage system and why it’s not possible to swim at beaches after heavy rain. We check in on the Central Interceptor upgrade and investigate great new plans for mussel restoration in Okahu Bay.

This series was first published on Stuff. It is made with funding from NZ on Air and GIFT Gulf Innovation Fund Together, a Foundation North Initiative.