The Belgian Shepherd, whose registered microchip name is Bella, was spotted drowning in the River Trent and dragged to safety by a woman near Long Lane, Farndon, at around 8.45am on Monday (January 6).
The dog had a carrier bag containing a large rock tied to her lead when she was found.
The dog is now recovering at a local vet.
A 31-year-old woman was arrested on suspicion of animal cruelty offences.
Nottinghamshire Police confirmed they have also arrested 32-year-old man.
PC Adam Pace, of Nottinghamshire Police, said: "We are still appealing for information about the circumstances of the incident, including how many people were involved.
"We are lucky that the kind member of the public found and rescued her. Whilst the dog is still quite poorly she has been showing some encouraging signs by eating, so hopefully she will be on the mend.
"If you saw anything, or have CCTV or dash-cam footage in the area, please get in touch on 101, quoting incident number 103 of 6 January 2020.
“Please be aware this is now an active police investigation and people must be careful what they post online as anything that reveals details of the investigation or those involved could be in contempt of court and it could be harmful to the investigation.”