Aquatic Pests

Aquatic pests!

Recreating in and around our rivers comes with big responsibility. As whitewater sports become more accessible and gear improves, more people are paddling and in more remote waterways than ever before. This is great for us, but if we’re not careful, it could be bad news for the spread of freshwater pest plants which can cause huge damage to river ecosystems and native flora and fauna. 

Didymo sometimes known as ‘rock snot’ is an alga that can form large blooms which look like soggy toilet paper. It grows on rocks and looks pinkish brown at the surface and cream in the water. Blooms typically occur in rivers with low nutrient concentrations meaning some of our most iconic and pristine rivers are most at risk. First reported in the Waiau River in 2004, it has sadly already invaded various waterways in the South Island. Thankfully it is not yet present in the North Island. 

Lake snow is a sticky, biological material made up of groups of algae that form colonies. Once lake snow gets into a waterway, it can take hold rapidly and form sticky, thick slime, the ecological impact of which is not well understood. Lake snow is now known from a number of large pristine lakes in Otago and Canterbury, as well as a couple of lakes in the North Island.

Pest plants such as Lagarosiphon (Oxygen weed) and Hornwort smother and suffocate aquatic life. They grow fast, displacing and shading our native aquatic plants, block waterways, and the rotting vegetation stops the flow of water which kills fauna and flora.

Removing these species once they have become established in a waterway is expensive and difficult so it’s best to prevent their spread. Weeds and algae can grab a ride on paddling gear and start new infestations. Didymo and lake snow are microscopic and can be spread by a single drop of water. Even if you can’t see it, you could be spreading it. The South Island is a controlled area for didymo meaning it is a legal requirement to clean all gear used in the water before going from one waterway to another.

Check out the video below for practical tips on how to ‘Check, Clean and Dry’ all your paddling gear whenever you move between waterways to prevent spreading pests. 

If you find unusual plants or algae you should note the location and take a photo or sample if possible. Inform your local DOC office or Regional Council as soon as possible or call the pests-and-diseases hotline on 0800 80 99 66.