Auckland's popular Mission Bay is once again open to swimmers.
Signs warning swimmers and beach-users of the poor water quality were taken down today.
Water quality testers say a dead animal or something similar caused the one-off closure of the beach this week.
Auckland Council's Safeswim picked up high levels of bacteria in the water on Wednesday during a weekly water quality test.
Swimmers were warned off using the beach due to the potential risk to human health.
Safeswim acting chief operating officer Ian Maxwell said testing yesterday showed the water quality had returned to normal and it was safe to swim.
"This appears to have been a one-off.
"We may never know what caused the issue. It's highly likely it was a localised ocean source, such as a dead animal or something similar."
The fail test result surprised the council because checks of the wastewater and stormwater networks did not indicate a problem, and no overflows had been reported.