Letchworth Outdoor Pool was broken into twice last week, with staff working to repair the damage caused before the pool opens this weekend for the summer.
A spokesman for owners North Herts Council said: "Sadly, we have had two break-ins.
"Quite a bit of damage has been done and staff are working hard to carry out repairs before we open.
"The police are helping with our enquiries and we have clear CCTV footage of all those involved.
"Please can parents warn their children of the dangers of breaking and entering?
"Swimming pools can be fun when used as intended, but it is dangerous running across the pool covers.
"We have security on site to protect the facility and public, but ask everyone to be careful and act responsibly."
Letchworth and Hitchin outdoor pools will open on Saturday, with Hitchin's pool closing on September 11 and Letchworth's pool open until September 30, after a successful petition to extend the season.
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