TIME BOMB: A local aquatic veterinarian warns the extended dry period has set up the Richmond River for a potential major fish kill.
TIME BOMB: A local aquatic veterinarian warns the extended dry period has set up the Richmond River for a potential major fish kill.

DIRE: Dry spell creates ‘ticking time bomb’ for fish kill

A LENNOX Head veterinarian has warned the extended dry spell has created a "ticking time bomb" for a fish kill in the Richmond River.

Dr Matt Landos, director of Future Fisheries Veterinary Service and associate researcher for Sydney University's Faculty of Veterinary Science, said the lack of surface run-off from rainfall has led to a build-up of "tonnes of monosulfidic black ooze" in the bottom of floodplain drains in the lower catchment of the Richmond.

"When run-off water remobilises this (black ooze) and it jets out of drains into the river, it deoxygenates the river rapidly and often fish cannot escape quickly enough and perish," he said.

"These were key contributors to the massive kills in 2001 and 2008.

"Much can be done to avoid these incidents with farmers working together with fishers.

"Unfortunately, since the 2008 kill, there have not been sufficient measures taken to alter the risks from drains, so I fear more major kills are inevitable if major rain falls suddenly on the Richmond floodplains."

Those two previous major fish kills led to tonnes of dead fish washing up in Ballina, with the accompanying stench lingering over the town.

The subsequent closure of the Richmond River to all forms of fishing on both occasions had a significant negative impact on the Ballina economy, with tourists staying away and commercial river fishers not being able to work.

The fish kills led to a series of public meetings over the years and expert think-tanks, as well as the introduction of Ballina Shire Council's Healthy Waterways program.

The floodplain drains Dr Landos is referring to are located in places like the Tuckean Swamp, Rocky Mouth Creek, Bungawalbin and Sandy Flat where natural wetlands have been drained for agriculture over many years.

Dr Landos said this drainage practice has led to the development of tonnes of sulfuric acid within acid sulfate soils, which leads to the formation of the black ooze in the drains.

Some work has been done to modify floodgates on drains to allow a slow release of the toxic ooze in a bid to minimise its impacts on the river.

Dr Landos said groups like OzFish and Landcare are working locally with farmers, councils and Rous County Council to try and improve the management of these drains.

He said the aim was to "reduce the risks to the health of the Richmond River, and avoid as many of the fish kills as possible".

There have been reports of saltwater species like flathead and bream being caught by fishers well beyond the usual tidal mark of the Richmond River.

The lack of freshwater coming into the catchment through rainfall has led to the saltwater flowing further upstream than usual.

Dr Landos said this was a natural process and aquatic ecology modifies slowly through this process.

However, Dr Landos said if there was "rapid significant rainfall" in the lower reaches of the catchment before the upper areas, many of these saltwater species may become trapped in freshwater and die.

"Saltwater fish won't survive in fully freshwater for long," he said.

"However, I expect this will be the minority of fish kills when it rains."