A mix of fat and wet wipes are what caused two wastewater overflows into Rotorua streams last weekend.
Rotorua Lakes Council advised the public to keep clear of three streams on the weekend after two separate incidents.
It warned people on social media wastewater may have entered Otamatea Stream via the stormwater network on Petrie St and possibly entered the Utuhina Stream below Martin St.
The second incident was at Linton Park, near Deborah Pl, and it was likely some wastewater entered the Mangakakahi Stream.
Since then the council worked to figure out the cause, and updated its website today.
"During the weekend two blockages within the wastewater network caused a back-up of sewage that overflowed from manholes, onto land and into nearby stormwater inlets," the statement on the website said.
These blockages were made up of a mixture of solidified fat and cleaning wipes "often referred to as 'fatbergs'."
Infrastructure Networks Performance Manager Eric Cawte said damage to systems and faults were expected from time to time.
"However, in these cases, the cause is something that is largely avoidable."
He said it was a timely reminder to the community that placing foreign items such as wipes into the wastewater network, even those that say 'flushable' on the packet, can result in significant issues for the infrastructure and, more importantly, for the environment.