Authorities say the bodies of birds and fish found at Tygum Lagoon, Waterford West last week died by “natural causes”.
Logan City Council’s environmental health team was alerted to the issue on 14 December.
Initial investigations found no evidence of contamination or poisoning, according to mayor Jon Raven, and the matter was referred to the Department of Environment, Tourism Science and Innovation (DETSI) for assessment.
“DETSI has since confirmed the deaths are due to natural causes and will not investigate further,” Cr Raven said.
“Contributing factors include low oxygen levels in the water caused by hot weather, recent rainfall and algae growth.”
A DETSI spokesperson said it did not investigate the issue.
Council said it suspects the birds were killed by botulism, which can increase in the lake during these warmer, wetter conditions.
“There is no risk to human health provided people stay out of the water,” Cr Raven said.
“Warning signs remain in place advising residents not to swim in the lagoon.
“The duration of this event will depend on weather conditions.”
Residents were warned not to touch any of the dead animals, with a contractor hired to remove them.
Earlier this year, residents were warned to avoid Tygum Lagoon while it was battling a blue-green algae infestation.
The local council said in July that the algae blooms, which occured at the same lake the year prior and are known for impact others in the region, were often observed after spells of hot temperatures and heavy rainfall.
Residents were also encouraged to report any further concerns to council on 3412 3412 or by emailing council@logan.qld.gov.au.
