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Why has all the water gone?

Every few years Lake Mulwala disappears. Find out why and when to catch this memorable sight.
Published: 12 May 2022

If you have been to Lake Mulwala in late autumn or winter, you may have timed it right to capture an eerie photo of an empty lake. 

You might have wondered why the water had disappeared and if it was going to come back – after all, Lake Mulwala is a popular spot for water sports and lake views. 

Lake Mulwala is on the New South Wales and Victorian border on the Murray River. Formed in 1939 when the Yarrawonga weir was built, the lake supplies water to towns and irrigators on both sides of the river. 

For more than 20 years the lake has had an ongoing struggle with an invasive waterweed, Egeria densa. It floats just below the surface, growing denser over time, blocking pipes and making it difficult to launch boats, fish, swim, or water ski without getting tangled. 

A closeup shot of a person holding a handful of Egeria densa, a common water weed in Lake Mulwala
A handful of Egeria densa at Lake Mulwala

Egeria is commonly found in home aquariums and ponds but has found its way to the lake where it thrives in the favourable conditions. It also competes with native under-water vegetation such as floating pondweed and ribbonweed, which are important for a healthy lake. 

Egeria is a weed that can’t be eradicated but its growth and spread can be managed by drying it out. That is why the water in Lake Mulwala is lowered every few years to expose the weed to air and winter frosts.  

By 2008 Egeria took up about 60% of the lake’s area.  

In 2009 the lake was lowered by close to 5.5 metres, exposing the lakebed where the Egeria was growing, successfully reducing the weed to 1% of the lake’s area. 

This method proved to be the only way of managing Egeria over the whole lake at one time. The lowering now takes place every 3 to 5 years depending on the density of the weed and weather conditions. 

In 2022, surveys show the weed at a high-density level so the lake is being gradually lowered from early May 2022, reaching 5 metres below the normal lake level by the end of June. The lake will remain low for about a month, exposing as much of the weed as possible, and will be refilled by the end of August. 

During winter there is a chance that rainfall could re-inundate some of the low-lying parts of the lake.

Over winter the disappearing lake is expected to draw visitors and local residents to capture a view of the original river channel, with ghostly remains of river red gums against a sunset or morning fog. 

Others may be hopeful to find their lost lures, hat or sunglasses. 

A previous drawdown of the water level in Lake Mulwala in 2018 exposing the lake bed and debris
A previous drawdown of Lake Mulwala in 2018

This operation is jointly managed by the Murray–Darling Basin Authority and Goulburn-Murray Water. 

Find more information about Egeria densa and the lowering of Lake Mulwala in this Goulburn-Murray Water factsheet.

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