More than £227,000 is needed to complete ongoing works at the NSC.
Tynwald will be asked to approve the funds for the flumes at this month's sitting - taking place next week.
The Department of Education, Sport and Culture says the overspend is because of ongoing problems regarding the leisure pool and flumes.
The facility has been closed since August 2018.
Braddan commissioners recruiting new top officer
One of the Island's largest local authorities is looking for a new clerk.
School meals meat bought locally, but may not be Manx
The government says although it buys meat for school meals locally, it can't guarantee it's Manx.
Manx Care staff suspensions cost £110,000, says minister
Health and Social Care Minister Claire Christian says 15 members of Manx Care staff have been suspended in the last four years, at a cost of around £110,000.
Commissioners worried about speed cameras on new 20mph signs
Could new 20mph sign poles be used to mount speed cameras in future?
Formula One Classic TT cancelled
MGP organisers say Friday's race schedule has been tweaked after delays to today's action on the Mountain Course.
Course due to close at 6pm, say police
Police say roads around the Mountain Course are due to close at 6pm for racing.
How can historic buildings be more eco-friendly?
How can historic buildings contribute towards net zero emissions?
Racing delayed again, with schedule update "imminent"
Race organisers say there's a further delay to today's racing.
