The dirty state of Lake Hayes' could be the result of
Coronet Peak's sewerage system and residential septic tanks,
Otago University freshwater scientist Dr Marc Schallenberg
Speaking at a recent Fish and Game Otago meeting in Dunedin,
Dr Schallenberg said the lake could be restored through the
introduction of Daphnia pulex, commonly known as the
The water flea would remove the reddish brown algal bloom
that was giving the lake its dark and dirty appearance.
However, even if the flea was introduced, external pollution
through the groundwater would have to be addressed by the
Otago Regional Council.
''Otago Regional Council is aware of what's going on here,
but there doesn't seem to be a lot of interest or ideas of
what we can do about it.''
He questioned whether fertilisers from the nearby Millbrook
and Hills golf courses, fertilisers from viticulturists, Lake
Hayes residential septic tanks and Coronet Peak's sewerage
system might have contributed to the lake's algal bloom
He estimated 20% of the lake's nitrogen pollution had come
Dr Schallenberg, a research fellow at the University of
Otago, had been studying Lake Hayes since 1995 and believed
the key to reducing algal bloom was to increase the number of
During 2010, the lake had been as clear as he had seen it and
he believed this was a result of a bigger population of the
foreign Daphnia pulex.
The clear water lasted two seasons but because Daphnia was
also a common fish food, the population had since died off
and the lake returned to its ''reddish brown'' colour, he
Perch had been eating the fleas and Dr Schallenberg suggested
reducing the number of the fish.
Because of its sediment makeup, the top layer of water in
Lake Hayes heated up during summer, while the bottom layer
did not change temperature.
He said this had a negative effect on trout because they
would swim at the upper level of the lake, where it could be
too hot for survival.
The warm layer prevented oxygen filtering down to the bottom
layer and that subsequently became anoxic, meaning without
oxygen, causing a chemical reaction that released phosphorus
''It's a pretty dire situation for a lake that had a major
commercial fishing aspect.''
Dr Schallenberg said options to restore the lake to its
original clean state for trout were: reintroducing
Daphnia, keeping a better eye on neighbouring
polluters, introducing chemicals or aerating the lake.