Jules Casey shared the footage to her Instagram account on May 9, showing her dive close to Rye Pier in Australia's Mornington Peninsula in Victoria.
Casey, who is based in the area, joked that the pufferfish looked like it was "whispering sweet nothings" in her ear, as it swam calmly beside her.
Casey often posts footage of what she sees below the waves at Port Phillip Bay to her Instagram account @OneBreathDiver, where she has over 90,000 followers.
Her work notes both interesting marine life, as well as dangers posed to underwater creatures by water pollution.
Credit: Jules Casey via Storyful