It may look strange, but scientists believe there is no danger posed by the foam coating the shores of Lake Rotorua near the Ohau Channel.
The froth has been washing up over the past few months and been particularly bad in the past couple of days.
Environment Bay of Plenty scientist Matt Bloxham said it was probably caused by an algae known as Kirchneriella, which was first discovered in the lake in 1998.
"Different species of algae proliferate at different times and this one typically has a higher biomass in winter."
He said because the algae reduces surface tension in the water, foam was more likely to be found in areas where there was substantial mixing and aeration of the water - such as the Ohau Channel.
