THE North Central Catchment Management Authority is monitoring Richardson’s Lagoon on the Murray River near Echuca as expected low water levels have resulted in the death of about 200 carp.
Richardson’s Lagoon is a regionally significant wetland and supports a high diversity of waterbirds and woodland birds.
The lagoon can receive water from the Murray River during very high natural flooding, but such occasions are rare, as it was disconnected from the river by levees built to regulate the system.
As a result, water for the environment is the only reliable way Richardson’s Lagoon receives flows.
NCCMA manager Trent Gibson said the lagoon was in a drying phase, an important part of ensuring its long-term health.
“Given Australia’s harsh climate, it’s understandable to think low water levels are a bad thing,” he said.
“In many cases, including at Richardson’s Lagoon at the moment, the exact opposite is true.
“Fluctuating water levels are great for birds and plants. Receding water gives opportunities for wading waterbirds such as herons, plovers and stilts to stalk the shallows for fish and insects.
“Surrounding trees also need to have dry feet from time to time, to help with seed germination and stop them from drowning. Wetlands across the region are full of dead eucalypts that have died because of historically high permanent water levels.”
Mr Gibson said low water levels also helped mitigate against blue green algae outbreaks.
“The lagoon has a long history of high-nutrient concentrations that have contributed to blue green algae blooms,” he said.
“To mitigate against further algal blooms and provide the best habitat available for the significant bird population, it’s important the water level in the lagoon fluctuates, with periods of both wetting and drying.
“Complete drying exposes the bottom of the lagoon to the air, allowing the algae to break down totally and turn into compost which is great for the soil. Complete drying can mitigate the risk of future algae blooms at Richardson’s Lagoon and allow many native wetland plants to complete their life cycles.”
NCCMA staff visited Richardson’s Lagoon on Monday and spoke with community members.
“Our estimates are there are about 200 carp that are dead or dying in a small section of the lagoon. It’s likely the deaths were caused by a mixture of low water levels and reduced oxygen, exacerbated by the recent heat.” he said.
“Richardson’s Lagoon is watered through a long series of pumps, pipes and channels, making it quite a journey for native fish to even get in.
“As expected, we didn’t see any native fish and we will continue to monitor the lagoon over the next few months, as we do with all the wetlands where we deliver water for the environment.
“As the larger pools draw down, we will monitor them and put a net in to see what, if any, large bodied native fish are there, and relocate them.”
Mr Gibson said the lagoon had been dry from 2001 to 2003 and 2007 to 2009, with low water levels in 2015.
“Spending taxpayer money or allocating water to save carp is not a priority of any CMA,” he said.
“And topping up Richardson’s Lagoon partially over summer increases the risk of algal blooms and could have a negative impact on vegetation.
“Permanent water levels can create wet deserts, wetlands that are dominated by one species of bird, fish and even water bug.
“Richardson’s Lagoon is home to about 50 different bird species, including four different types of cormorants, great egret, white-necked heron, nankeen night heron, ibis, royal and yellow spoonbills and brolga, and the community and the CMA is keen for it to stay that way.”
People are advised to avoid contact with the dead fish and not to eat them.
While the water itself is safe, as a precautionary measure people are asked to avoid swimming or wading. An odour may also be present.