Sunnah Khan was among ten people who were involved in an incident on the water on Wednesday afternoon (31 May).
On social media, the mother of the girl said she was "so well loved and well liked".
A tweet reads: "On Wednesday I lost my beautiful daughter at Bournemouth beach. Sunnah was so well loved and well liked. No parent should ever have to go through what her dad and I are going through. We love you so much baby girl."
On Thursday night, a pleasure boat was impounded by police who it's thought are looking into the vessel as part of their investigation into the deaths.
ITV News understands the Dorset Belle was in the vicinity of the water shortly before the ten people experienced problems in the water.
A man in his 40s, who was on the water at the time, was arrested on suspicion of manslaughter and has since been released under investigation.
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