Lake system

Background

The RBG lake system includes Central Lake, Fern Gully, Nymphaea Lily Lake, Ornamental Lake and the surrounding catchments. The Ornamental Lake and Fern Gully are the remnants of a natural water system in the RBG Melbourne, which pre-dated European settlement of Melbourne. The Ornamental Lake is the closest and largest fresh waterbody to the Melbourne CBD, and originated from a natural lagoon that was likely used as food source (particularly Short-finned eels) by the local aboriginal people. Today, the lake system continues to provide important habitat for indigenous aquatic plants, water fowl, fish, turtles and other organisms.

Blue-green algae

Since de-silting of the Ornamental Lake in 1982-83, blue-green algal blooms have regularly appeared during the warmer months of the year. Blue-green algae (actually cyanobacteria) are a natural inhabitant of water bodies, but an absence of water plants (macrophytes), high nutrient levels, still water, and warm, sunny weather provide the recipe for an explosion in population or ‘a bloom’. While unsightly, these blooms are also potentially toxic and reduce the Lake biodiversity.

Establishment of indigenous water plants

In 1999-2000, works began to restore a collection of Melbourne-indigenous flora at Long Island. (This area is all that remains of the original south bank of the Yarra River, before the course of the river was relocated to the north of the present day Gardens in the late 1800’s). Further to establishment of macrophytes as part of the Long island project, additional planting has occurred at key areas around the Ornamental Lake, to promote biodiversity and ultimately aim to limit the frequency and severity of algal blooms.

From 2009, the establishment of this planting, and the appearance of additional macrophytes appear to be having an influence on the timing and duration of blue-green algal blooms.

Research Projects with Monash University

Continuing since February 2002, the Gardens has also enjoyed a research partnership with the Water Studies Centre at Monash University that has looked at the cycling of nutrients from the sediments and how this fuels algal blooms. Student projects have produced high-quality publications which have significantly contributed to our understanding of lake conditions. Not only has there been direct research projects studying the hydrodynamics of the Ornamental Lake, but it has also been used as urban water body to inform other student research being conducted at the WSC.

In early 2010, the School of Biological Sciences, Monash University in partnership with RBG Melbourne began supervising student research into the aquatic biology of the Ornamental Lake. One current research projects includes studying the interactions of macrophytes (water plants), zooplankton, fish and algae.

Turtle Survey

A turtle survey was undertaken in November 2010 to provide baseline data for researching turtle populations in other urban wetlands around Melbourne. Surprisingly, while it was known that Common Long-necked Turtles (Chelodina longicollis) occur in the lake, no one had realised that there were actually two species present with Murray River Turtles (Emydura macquarii) also being found.

Working Wetlands

In 2010, works began to construct Working Wetlands. Funding has been generously provided through funds from the Victorian Government, a grant from the Myer Foundation, and support for the planning process from Melbourne Water. This project aims to improve the ecological condition of the lakes system, through the harvesting and treatment of additional stormwater supply to the Ornamental Lake. The water of the RBG lakes system will then be recirculated through wetlands to provide unsuitable conditions for the blue-green algae by reducing the amount of nutrients and increasing the movement of water 

Fact sheet

Blue Green Algae (MS Word - 257 kb)