Nitro, Mustoes and one other undisclosed agency pitched for the pan-European fruit-flavoured sports drink business. Nitro is now understood to be working on the soft drink's launch campaign, which will air this summer.
Coca-Cola appointed Mustoes to handle the business at the start of this year (Campaign, 27 January).
A spokesman for Coca-Cola said: "The company is looking at plans for Aquarius across Europe. We're not in a position to confirm any plans at the moment."
Aquarius' advertising is likely to focus on its health and fitness benefits.
The drink's launch ties in with Coca-Cola's decision to refocus its marketing on health and performance drinks.
The review does not affect Aquarius' media planning and buying account, which is handled by Vizeum.
Aquarius launched in Japan in 1983 as a grapefruit- flavoured drink.
Orange and lemon variants have since been added to the range.
Launched in Spain and Portugal in 1991, Aquarius is now marketed in 15 countries in Asia and Europe.