Palmerston North's Freyberg pool was closed on Friday after a poison threat. It was cleared and reopened on Saturday (file photo).

Police are still investigating an online threat made against a popular Palmerston North swimming pool suggesting someone had dumped 1080 pellets in the water.

The pool was closed on Friday evening after the threat but testing revealed the Freyberg Pool was safe for public use and it reopened at 8am on Saturday.

A police spokeswoman said police were investigating the incident and inquires were ongoing.

The city council closed the pool on Friday evening after it "became aware" of a social media post that pellets had been placed in the pool and at "undisclosed public parks".

"Although the... threat is the action of one person on social media, we have taken immediate action and closed the Freyberg pool for water testing by MidCentral District Health Board," said council spokeswoman Sacha Haskell.

"Police have been informed and are checking on the individual concerned and validity of these threats."

Council officials will work with police as the threat is investigated. The council is asking people who see suspicious substances in parks and on walkways to contact its call centre – 1080 pellets are green or blue.

The council call centre's number is 06 356 8199.