Biosecurity NZ says if a pest seaweed gets out of control, it could take over our native sea plants

Strict rules are now in place in an attempt to stop the spread of an invasive seaweed.

It's now illegal to take seafood from Great Barrier Island at Blind Bay and Tryphena Harbour, and anchoring requires a permit.

Biosecurity NZ's Director of Readiness and Response John Walsh says movement along the seabed risks picking up fragments and moving them elsewhere.

He says the worst that could happen is the pest seaweed could smother our native sea plants.

People can still swim, dive and paddle in the area - but not drop anchor.