The weed cordon that excluded boats from the Motuwhetero arm of Lake Ōkataina last week has been removed.

Two weed cordons were originally erected in Lake Ōkataina to help contain hornwort.

The weed, one of New Zealand's worst freshwater weeds, reach as high as a three-storey building (10m), the Bay of Plenty Council says in a statement.

Hamish Lass, the regional council's senior projects officer says hornwort was first discovered in the lake in 2010.

'Since then, we have invested a great deal of time and resources to contain the hornwort using a combination of herbicide and hand removal.

'The use of the weed cordon at the southern end of the lake, which excluded boats from the area while it was being treated, has been instrumental in containing the spread.

'The fact that we are now in a position to remove it represents a significant step in eradicating hornwort completely from the lake,” he says.

Once in a waterway, hornwort can quickly form dense weed beds that outcompete and smother all other freshwater plants, the council's statement says.

It can block waterways and impact on boating, fishing and other lake uses.

New hornwort plants can form from even tiny pieces of the easily broken stems, causing new infestations when those fragments are carried to other waterways via outflows, birds, fishing equipment and boat movements.

Lake users should check, clean and (when practicable) dry their boat, trailer, prop, fishing and sporting equipment when moving from one waterway to another, anywhere in the Bay of Plenty.

To further protect the lake from new weed infestations, the second weed cordon at the Lake Ōkataina boat ramp will remain.