Winchester's main indoor sports centre will close for three months next year as part of a £1m refurbishment.
Thousands of people will be forced to use facilities in Eastleigh, Basingstoke, Romsey or Southampton during the closure.
Council chiefs say the River Park Leisure Centre needs a major overhaul otherwise its future is jeopardised.
But today the chairman of the Winchester Penguins swimming club said news of the closure had come out of the blue and could be disastrous.
Stuart Ward said: "It could be catastrophic if it is at the wrong time, disrupting preparation for the county championships and galas. At best it will be very inconvenient.
"I didn't know anything about this. I'm quite surprised. I will be seeking a meeting with the centre as soon as possible."
Mr Ward added the financial health of the Penguins might be affected.
"It becomes a cash flow issue for us too in the running of the club," he said.
The city council wants to replace important equipment such as boilers, filters and the heat and power unit. The swimming pool requires a new roof as the insulation has become saturated with water.
It hopes to keep some areas open that are unaffected by the works such as the health suite and some dryside facilities.
A report to the city council cabinet on Tuesday (APRIL 20) estimates the essential work will cost around £1 million. Exact figures will become available once the tendering process starts and the cabinet gives final approval.
The city councillors will have to decide whether to spend another £500,000 on other improvements including new poolside ventilation, upgrading the changing rooms, showers, toilets, CCTV, intruder alarms and laying a new artificial turf pitch.
The work was always planned because the efficient working life of much of the machinery was estimated at about 15 years. The leisure centre originally opened in 1974, expanded in 1981 and was rebuilt after a massive fire in 1987. It reopened in 1988.
The company that operates the centre, DC Leisure, was told that the closure would happen in 2005.
A report by Steve Tilbury, director of community services, said the council will pay for the work but DC Leisure will have to bear the loss of income.
The closure was expected to be around 12 weeks but until the council decides what work will be done the exact time is unclear.
Of the essential work, Mr Tilbury said: "These are works which must be undertaken if the future operation of the building is to be secured. If they are not carried out then a failure of plant will occur and would result in closure of parts of the centre.
"The council has very little choice but to proceed with the essential items in 2005 as planned. Not to do so would place the operation of the centre in jeopardy.
"An unplanned closure due to plant failure would be costly and very inconvenient."
Most of the essential work will not be seen by the public although it will improve plant efficiency, clarity of the water and safety.
Mr Tilbury said upgrading of the changing rooms would counter the complaints from the public about poor air circulation.
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