Ministry for Primary Industries On Farm Support Otago regional adviser and dairy farmer Sandra Campbell said rats had eaten holes in the corners of the liner of her eight-year-old effluent pond and had made themselves homes under the lining.
A new liner will be installed in the 30m x 30m pond on her Clifton dairy farm this week.
She recommended using a contractor who was a "one-stop shop".
"There is a lot of moving parts."
Mrs Campbell said she had budgeted $70,000 for the pond, including replacing the liner and installing drainage.
"I’m hoping for $60,000 — the liner was $30,000."
However, the cost to empty the effluent from the pond remains unknown.
"It is going to take some getting out."