Yesterday outdoor rangers had to close off Bonnyfield Nature Reserve pathway and alert environmental experts after the substance was discovered in a pond.
The path, near Emma’s Way towards the eastern entrance of the Bonnybridge reserve was temporarily closed to the public as Scottish Water and the Scottish Environment Protection Agency (SEPA) investigated the matter.
A SEPA spokesman said: “We received notification from Falkirk Council that an unknown substance had been discovered in the pond at Bonnyfield Nature Reserve, Bonnybridge. We attended the site to carry out an investigation alongside Scottish Water.
“The substance has been identified as sewage which had overflowed into the sustainable drainage system as a result of a blocked main sewer. We are satisfied the sewage remained in the sustainable drainage system and will not have a significant impact on the environment.
“We understand Scottish Water are currently carrying out work at the site to unblock the sewer.”