Biosecurity New Zealand is teaming up with Mana Whenua and Northland Regional Council to stop the spread of exotic caulerpa  seaweed

Divers found 23 rugby fields worth of the fast spreading seaweed which can smother other native species.

An anchoring and fishing ban will be put in place this week at Omakiwi Cove in the Bay of Islands.

Mana Whenua has also put a rahui on the area.

Deputy Director General Stewart Anderson says boaties should be aware of it in other areas too.

He says boaties should take photos of the seaweed and send the coordinates to Biosecurity New Zealand.