Improvements to the new artificial surf reef at Boscombe on the Dorset coast, which has been deemed sub-standard, may not be carried out until 2011.
Experts who assessed the quality of waves at the reef found it achieved only four of its 11 objectives.
The New Zealand firm that built the reef disputes the findings and is due to visit the site next month.
Roger Brown, of Bournemouth Borough Council, said any improvements may not be carried out until next spring.
A team from Plymouth University studied the quality of the reef's waves and the number of days suitable for surfing over six months from last September and concluded it was sub-standard.
The council said it would withhold a £150,000 payment from creator ASR Ltd until it was satisfied it worked.
The study collected data from on-site cameras and location visits
Mr Brown, head of leisure services, said: "If we know with confidence that we can't guarantee that the works would come in and be completed before the end of British summertime, the end of October, we will not let ourselves get into the situation that we were in two years ago during the construction.
"If we find ourselves in that situation, we would undertake to do the works in the spring of next year."
ASR denied the reef failed and said it was only one of the criteria - the wave lengths - which it had not met.
But it said it would work with the council to make "enhancements to the reef".
The £3m construction opened in November after a delay of more than a year and at nearly double the proposed cost.
There has been a mixed response to the reef's success from surfers.
It was created to improve surfing conditions using 55 sand-filled "geotextile bags" which are 225m (740ft) out to sea.