Barely visible here beyond the rocks is the Nevis, a remote river that takes over an hour drive on a dirt road and over 15 river crossings to reach. We didn't see one person all day. It is one of the few rivers that isn't didymo affected. Didymo is a freshwater algae first discovered in South New Zealand rivers in Oct. 2004. It is most readily spread on contaminated gear used by river users such as fishermen and kayakers. Its origin is northern US and Europe. The main difference between didymo and native species is the way it feels. Native algae feels slimy and will break apart in your fingers, whereas didymo is strong and feels like wet cotton wool. Didymo is an unwanted organism under the Biosecurity Act 1993. It is an offense to knowingly spread an unwanted organism with penalites of up to 5 years imprisonment, and/or a fine of up to $100,000. Gear and clothing is carefully cleaned and dried before entering the water.