Hey Leanne,
I have an ancestor who also died in a drowning, and like you I suspect this as I have found articles on Trove that lead me to this end. Also like you, his wife re-married and stated herself as a widow, but I there is no record of his death as there was never a body found.
It is a very frustrating thing when you are 99% sure that the ancestor you are interested in is the one that drowned, but there isn't the legal certification to prove it. If possible, can you let me know if you find anything at PROV? My ancestor died in NSW, but any leads on if you can find certificates for drowning deaths would be great.
Thanks,
Ash