The officer has been accused of altering a police statement to say that effluent was leaking from a Riverton stock truck and later of making false statements in a written case against Twin Peaks Farming Ltd for discharging sediment.
Chief executive Rob Phillips announced yesterday that he had instructed environmental lawyer Karenza de Silva to undertake a comprehensive audit of Environment Southland's compliance division.
"Prosecutions are an essential part of our compliance activity, particularly where there has been a serious breach of the law, a regulation or a rule," Mr Phillips said.
"Everyone needs to be confident that compliance action is based on sound processes that have been carried out with integrity," he said.
An Environment Southland spokeswoman told the Otago Daily Times the document the officer had been accused of altering was not a police statement as had been reported and was instead an "Environment Southland work sheet".
"The allegation that a police document has been changed is completely incorrect,"she said.