Douglas Council says opening the splash park three weeks earlier each summer would be too expensive because it would have to pay staff extra.
The local authority's Regeneration and Community committee discussed the issue at its last meeting, when it was suggested the facility in Noble's Park opened on Friday, May 1 instead of Saturday, May 23.
Councillors heard the splash park is run by staff working overtime, and bringing its opening forward would cost £1,500.
They voted to keep the current schedule and review the decision in a year's time.
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