In March this year the Biggs Avenue Lake suffered a large scale fish kill.
Upwards of 54,000 fish are estimated to have died, and a report conducted by DigsFish has revealed this was due to low levels of dissolved oxygen (DO).
Dr Ben Diggles from DigsFish was notified by concerned residents on Saturday March 30th of the fish kill. Over the next two days he monitored the lake and took samples to determine the cause.
The resulting report stated “Gross examination of several dying fish failed to detect parasitic diseases that can sometimes be associated with multi-species fish kills. Instead, measurements of dissolved oxygen (DO) found that lake water was down to less than 5% oxygen saturation (0.34 mg/L) in many places along the lake edges. This is an extremely low oxygen level that is acutely lethal to virtually all species of finfish.”
DO concentration levels were affected by an algal bloom which had developed in the lake. This was caused by a build-up of nutrient rich storm water from a blockage of an inlet pipe which prevented tidal flushing.
During the fish kill Moreton Bay Regional Council (MBRC) staff placed supplemental aerators around the southern end of the lake which, according to the report, created a limited effect oxygen refuge.
“Overall, several hundred larger “broodstock sized” fish of various species were evacuated by local residents, recreational fishers, OzFish Unlimited volunteers and MBRC workers. It was noted that the symptoms of respiratory distress abated and fish recovered quickly after placing them into water containing normal oxygen content.” Said the report.
Management and protection of these crucial fish nurseries not only affects the fish population but other native wildlife.
“I note the recent widespread community concern about iconic local pelicans and whether they have a place to sit on the Bribie Bridge. While this is laudable, my main concern is that if we continue to allow mismanagement and destruction of our critical fish nursery areas, our beloved pelicans, and other water birds will have nothing to eat. If our waterbirds starve, they will disappear, so let’s get things into perspective and work hard to try to save our vital underwater resources (i.e. fisheries habitats).” Said Dr Diggles.
The DigsFish report was conducted as a voluntary effort and has been provided to MBRC along with recommendations to prevent further large scale fish kills occurring.
Recommendations in the report involve improving MBRC responses to fish kills in the region, removing the excess of anoxic sediments in the lake, increasing the reliability of the supply pipe’s infrastructure and restoring natural tidal flushing and fish passage.
If changes are not made Dr Diggles has said “Based on past experience, we can expect a 95+% fish kill at least every decade or so, or even more frequently depending on the effectiveness (or lack thereof) of council maintenance of the existing system.”
The following statement has been provided by a Council spokesperson on the incident:
“Following the incident in March, Council conducted an assessment of the lake’s circulation system and undertook water quality and algae tests. These indicated several factors that resulted in the lake containing nutrient-rich stormwater for an extended period, leading to an algal bloom. The algal bloom affected dissolved oxygen concentrations in the lake, which contributed to the fish kill.
Council has committed to improving the lake system which plays an important role in stormwater management and flood mitigation. Council is currently considering options to improve the functionality of the constructed lake, and will continue to keep residents up-to-date as this project progresses. More information is available on Council’s website.
The report produced by Digsfish Services was not commissioned by Council. However the report has been provided to Council and Council will consider the findings alongside other feedback received from the community.”
On Tuesday March 16th, Dr Diggles received a personal response from Mayor Allan Sutherland.
In the letter the Mayor has said “I am advised that the Recreational Fishing Grant Program provides funding to support activities and projects that enhance recreational fishing in Queensland. DigsFish has suggested that funding via the program be sought for the implementation of automated flood gates as a mechanism to allow fish passage to and from Beachmere Lake. I understand that this is one of a range of options that may be suitable for implementation at this location.
I am further advised that Council’s Drainage, Waterways and Coastal Planning and Environmental
Services departments are working to identify practical options to better manage fish populations
in the Lake. An Options Assessment will be undertaken to identify a preferred fish management
strategy in consideration of a range of issues at the site including elevation relative to sea level,
existing tidal exchange processes, flooding, local government planning controls, state approvals
and community support.
Once a preferred approach has been identified, Council would be in a better position to pursue,
as appropriate, funding support from the state via the Recreational Fishing Grant Program or
Council will advise DigsFish and the community of the outcomes of the Options Assessment and
our preferred course of action to better manage fish populations in the Lake and, as appropriate,
the funding mechanism and partnership arrangements Council could seek to pursue to assist in
project design and delivery.”
From this response Dr Diggles feels MBRC will continue to refuse to liaise with independent fish passage experts whilst considering options for lake management.
“Unfortunately, leaving fish passage decisions to engineers is what got us into the mess at Beachmere Lake in the first place.” Said Dr Diggles.
Dr Diggles urges locals wanting to help to “read my report and make up their own minds - then let their local councillor know what they think. They should also be very careful about what goes down local drains - no more emptying grass clippings or disposing of fertilizers or other nutrients or pollutants into the drains, or spraying chemicals near gutters or drains, as these all will end up in local waterways next time it rains.”
For those wanting to read the DigsFish report it is publically available on the DigsFish website - http://digsfish.com/digsfishbeachmerefishkillreportfinal.pdf