FAST-tracked test results show algae levels remain high, meaning Lake Borumba will not be re-opened to water-based recreation ahead of Australia Day.
The lake is currently closed to recreation activities due to the presence of blue-green algae. The latest water quality samples indicate algae levels remain too high to re-open the lake.
Seqwater chief executive officer Peter Dennis said the health and safety of visitors was a key priority.
"We have been contacted by a family who reported falling ill after swimming in Lake Borumba at the start of last week, just before the closure," Mr Dennis said.
"We have a duty of care to safeguard other visitors from exposure to blue-green algal blooms and the health conditions which can result.
"There are a number of symptoms associated with exposure to blue-green algae such as abdominal cramps, diarrhoea, vomiting, nausea, rashes, swelling, sores, irritation, earache, eye irritation, cough and congestion."
Mr Dennis said Seqwater recognised the impact of water-based recreation closures on the community, including local business, and would continue to accelerate its sampling and analysis in an effort to re-open the lake as soon as it is safe to do so.
"Seqwater considers the National Health and Medical Research Council guidelines for recreation management and the Department of Environment and Heritage Protection blue-green algae guidelines, in determining whether to restrict access to water-based activities when our regular water testing shows algae levels are high," he said.
"Recreation is a core service of our business and we have specialist in-house water quality expertise to apply the best science and knowledge available. As such, our standard of testing and monitoring is high.
"We will re-open the lake as soon as it is safe to do so."
The Seqwater website (www.seqwater.com.au) and Facebook and Twitter pages will be updated as conditions change at Lake Borumba.
Visitors are asked to observe signage in place at Lake Borumba and follow the direction of staff.
For more information, a fact sheet on blue-green algae is available on the SEQ Water website.