Newcastle City Council announced last year that the pool could close as part of a bid to save ??90m from the council's budget for 2013 to 2016.
As part of a lobby against the cuts, more than 100 people filled the pool to its maximum capacity in a 'swim-in' on Saturday afternoon.
They were watched by hundreds of spectators with banners.
Newcastle Amateur Swimming Club, which has 200 members, said closure would leave them without a base.
Louise Graham, head coach at the club, said: "I find it hard to believe that the council is planning to evict the club and all the other pool users.
"If the pool closes, Newcastle will have lost a crucial sporting asset as well as a building of major historic importance in the heart of the city."
The club, created in 1977, has started a social media campaign, Save Newcastle City Swimming Pool and an online petition which has nearly 2,000 signatures.
The council said the combination of the investment needed, plus a nearby alternative pool, led them to propose the closure which is predicted to save ??275,198 in 2013 and ??285,198 in 2014.
More than 171,486 people used the pool in 2011/12.
Newcastle City Pool employs 23 members of staff.
Hundreds of people have taken part in a protest against the proposed closure of Newcastle City Pool.