Rock Snot.

Thank you America, or should I say American anglers. Someone brought Didymo to NZ about 8 years ago. It looks like snot and has infested our rivers, in this case about as high up as you can go. We now are encouraged to 'check, clean and dry' when moving between river catchments to prevent the spread. Nobody seems to talk to the Canadian Geese that also infest this area.