The Dolphin sports centre in Haywards Heath is to be given a £2.3 million upgrade from this month.
Work is due to start on a major redevelopment of the centre on November 27 to bring it up to the standards of Burgess Hill's Triangle centre.
The project will include a new gym featuring 70 workstations, a free weights area, a spa, sauna and steam rooms, four treatment rooms, a dance studio and a caf bar.
Creche facilities will be improved, and a boom will enable the pool to convert from 33 to 25 metres for competitions.
Mid Sussex councillor Mike Gilks said: "I came up with the idea of the leisure department borrowing the money from the council and then paying it back.
"This will hopefully reduce the net cost of running the centre.
"The whole concept of The Dolphin was to provide a decent facility at a reasonable price which will pay back the council.
"Once that is paid back it will be a substantial advantage to the taxpayer. Hopefully it is a win-win situation."
Councillor Gilks added: "This facelift for the Dolphin means provision of a very much needed health and fitness facility which ties in with our views on health and the support of health to encourage people to be more active and have facilities for youngsters."
Work is expected to last several months. But the council is determined to keep the centre open for business.
Coun Gilks said: "As far as is humanly possible the existing users will be disadvantaged as little as possible."
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