Introduction

A four day search conducted by a team of divers from the Department of Conservation’s Te Anau Area Office have found no sign of the invasive aquatic weed Lagarosiphon major (oxygen weed).

Date:  02 July 2012

Diver searching for Lagarosiphon.
Diver searching for Lagarosiphon

A four day search conducted by a team of divers from the Department of Conservation’s Te Anau Area Office have found no sign of the invasive aquatic weed Lagarosiphon major (oxygen weed).

Sites within Lakes Te Anau, Manapouri, Monowai, Hauroko and Mavora Lakes, as well as some high risk river and stream locations were surveyed by the team as part of an annual surveillance programme, co-funded by DOC, Environment Southland and Meridian Energy. In total, 22 sites were inspected.

Lagarosiphon is a fast growing submerged weed which forms dense mats. DOC Te Anau Freshwater Ranger Lyndsay Murray said these can block waterways and hydro-electrical dams, and smother, exclude and eventually replace native aquatic vegetation. Lagarosiphon can also prevent fishing, boating and swimming activities. 

Lagarosiphon was first discovered in the Rotorua Lakes in the 1950s. Since then it has spread to many waterways in the south (including the Oreti and Waihopai river’s in Southland), becoming a major problem in many Central Otago and West Coast lakes, but thus far has not made it in to Southland and Fiordland’s major lakes.

The sites chosen focussed mostly on boatramps due to the increased risk posed at these points of entry. Lagarosiphon is commonly spread by contaminated boats and trailers, or diving, swimming, fishing and ski gear. Commonly used as an aquarium plant, it has also been known to become established in waterways after people have emptied the contents of fishtanks into the water as well.

Lagarosiphon is extremely hard to get rid of once established, therefore the principal objective of DOC’s Southland Conservancy is to prevent it’s entry to any of the lakes in the area.

Whilst the results are pleasing, the recent find of Lagarosiphon in Lake Waikaremoana and Lake Kuratau in the North Island (in March and April respectively) during similar surveillance programmes serves as a reminder for boaties and waterway users to keep vigilant about the risk of transporting lagarosiphon on their gear.

Before leaving the boat ramp, it is important to clean any weed off your boats’ hull, motor, intake and trailer as well as making sure all fishing, swimming, kayaking and dive gear are clean. These small steps will help to ensure that Southland’s lakes continue to remain in the healthy state that enables us to enjoy these activities.

 

Contact

Lyndsay Murray - Freshwater Ranger
Ph: +64 3 249 0200
Email: lcmurray@doc.govt.nz

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