Lake Macdonald, near Noosa in
southeastern Queensland, holds 8000 ML
of drinking water for the region and
provides a significant wildlife refuge.
The lake has been infested with cabomba
for about ten years and now 75% of its
surface area (about 180 ha) is covered by
the weed. Control options are limited by
the fact that herbicides cannot be used
on the town water supply. Drawdown
is not an option as the lake is part of the
town’s drinking water supply, is habitat
for the endangered Mary River cod and
provides local recreational opportunities
such as boating and fishing.
While it has been accepted that the weed
will never be eradicated, the local shire
and community groups have adopted
an integrated approach, focusing on
actions to reduce impacts and prevent
the spread. The control program
includes: constructing sealed boat ramps
to prevent snagging of cabomba on boat
trailers; organising education campaigns
to promote decontamination of vehicles
and equipment; restoring and
maintaining riverbank vegetation; and
investing large amounts of time and
money in mechanical removal and
limiting the flow of nutrients into the
system from catchment land uses.
The council purchased a mechanical
weed harvester for $260,000, which is
capable of cutting and collecting weeds
down to about 1 m below the surface.
It compacts the cabomba to prevent
nutrients leaking back into the lake. The
waste can then be disposed of safely.
The first cut with the harvester grew back
within three weeks, but after the second
run the plant responded at a much slower
rate. The aim is that continual cutting
will weaken the cabomba to such an
extent that native water plants can
compete for space. However, after
several years this has not yet happened.