Lake snow


Common names: Lake Snow

Botanical name: Lindavia intermedia

Management programme: Organisms of Interest


Lake snow is a sticky, biological material made up of groups of algae that form colonies. Lindavia intermedia are the algae species responsible for creating lake snow.

Research has found that the genetic source of Lindavia intermedia (the algae responsible for creating lake snow) is highly likely to be from outside NZ.

Genetic testing of lake snow samples by the report author, Landcare Research, found that specimens those from Lake Youngs in Washington State (USA) and all NZ lakes were identical in more than one respect.

It has also been found in Lake Coleridge in Canterbury. In the past, it has been found in Lake Benmore, Lake Aviemore and Lake Hayes in the South Island and Lake Waikaremoana in the North Island; however, it does not appear to be present in these lakes today.

Why is it a pest?


Lake snow

Lake snow

Organism of Interest

This plant has not been accorded pest status in the Otago Regional Pest Management Plan (2019-2029) but is recorded as an Organism of Interest (OOI) for ongoing surveillance or potential future control opportunities.


How does it grow?

There are some suggestions of the reasons behind the rise of lake snow algae, which are linked to both natural and human-made influences. For example:

Climate change effects
With a changing climate, any increase in temperature, even a subtle one, may produce conditions that favour the growth of different species of algae.

Land-use changes and increased nutrients
Many Central Otago lakes have very low Trophic Level Index (TLI) values, which indicate low levels of nutrients and algae, a sign of good water quality. Because of this even very slight increases in nutrients in a lake can result in marked changes in the algal community.

Water fleas
Water fleas (Daphnia spp.) in the lake may preferentially graze on an algae that typically competes with lake snow algae. The introduced North American water flea Daphnia pulex is a more efficient consumer of these competing algae than the New Zealand native water flea, Daphnia carinata.

This increased grazing pressure from D. pulex may remove more competitor algae than normal, creating a vacancy in the environment for lake snow algae to get the upper hand.

Is it harmful?

Although it is not toxic and poses no known human health risk, it is creating costly problems for water users. If it gets into the residential water supply, lake snow causes blockages, clogs filters and household appliances connected to the system.

On the lake, fishermen may find the algae accumulates on their fishing lines and lures. It can also stick to boat hulls and equipment, wetsuits and your skin or hair if you come in contact with it.

What are we doing about it?

Recent findings will give impetus to multi-agency efforts (ORC, Environment Canterbury, Environment Southland, and the Ministry for Primary Industries) to identify appropriate ways to manage lake snow in the southern alpine lakes and elsewhere in NZ.

The work stream will focus on:

  • The origins of the species 
  • Researching the drivers of the dominance of lake snow in lakes
  • The development of technologies for effective sampling and monitoring of lake snow
  • The development of methods to stop the spread of lake snow between lakes.

We are currently running a comprehensive lake monitoring programme that will give us detailed information on how many nutrients are in the lake and the overall trophic state of the lakes. 

The ultimate aim of this research is to determine whether it is possible to manage lake snow.  

Citizen Science - lake snow encounter form
Have you had an encounter with lake snow? Report it here as part Otago’s citizen science. Submit your info every time you encounter lake snow and encourage your friends and family to do the same. Lake snow encounter form

How can you control it?

Freshwater pests, including lake snow or didymo can be spread by a single drop of water or plant fragment. With limited control tools available for some aquatic pests, and none at all for others, it is very important to limit and prevent it from invading other water bodies. We employ a Freshwater Biosecurity Advocate to travel around the lakes and popular aquatic recreational sites, spreading the Check, Clean, Dry message.

If you are moving your boat from one lake to another, you must always Check, Clean, Dry any equipment that comes into contact with the water, between every waterway, every time.

To prevent the spread of freshwater pests, including lagarosiphon, whenever you move between waterways you must check, clean and dry any equipment that comes into contact with water. 

Before you leave any river or lake: 

Check — remove any plant matter from your gear and clothing and leave it at the site. Don’t wash plant material down the drain.  

Clean — soak or scrub all items using one of the below treatments: 

Cleaning option 



Dishwashing detergent or nappy cleaner 

10% mix (1 litre to 10 litres of water) 

Soak or spray all surfaces and leave wet for at least 10 minutes 


2% mix (200mls to 10 litres of water) 

Soak or spray all surfaces for at least 1 minute 

Hot water above 60°C 

Soak entire item 


Soak for at least 1 minute 


Hot water above 45°C 

Soak entire item 

Soak for at least 20 minutes 



Until solid 

Note: 60° C is hotter than most tap water; 45°C is uncomfortable to touch. Allow longer times for absorbent items.


Dry ensure your gear is completely dry to touch, inside and out, then leave to dry for at least another 48 hours before you use it. Didymo can survive for months on moist gear.   


If it’s wet, it’s a threat.  


Make sure you don’t spread any aquatic pests by following the Check, Clean, Dry method.  

Click here for more information on Check, Clean, Dry. 

You can also help by letting us know if you find lake snow in an Otago lake or waterway other than Wanaka, Wakatipu or Hawea. Report it to us on 0800 474 082.


Workshops and reports

ORC commissioned Landcare Research to research the origins of lake snow (Lindavia intermedia) so a multi-pronged effort to blunt the nuisance effect this pest weed has on recreational users of Otago’s pristine Southern Lakes and nearby householders could be embarked on.

We held a community event to explain the findings of this research report and outline the next steps. You can download the presentation from this event below:

Public information session - presentation 4 October 2017

On 13 September 2017, ORC’s technical committee received the Landcare Research report, and an accompanying staff report summarising the report findings and providing a timetable for next steps.  

Landcare Research paper

Technical Committee staff report - 13 September 2017

On 22 March 2017, ORC’s technical committee received a report from Ryder Consulting on a lake snow experts’ workshop held in Wānaka in December 2016, and an accompanying staff report. It was at the workshop that the decision to commission the Landcare Research report was made.    

Lake snow technical workshop report

Technical Committee staff report - 22 March 2017

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