Burglary update - advice needed

Hey fellas - back in January, I posted about my house being broken into, a gun and some jewelry being stolen.

Well, I learned today they arrested three pieces of shite for my house and about 10 others. I knew they arrested these guys a while back, but apparently they broke into so many homes, they couldn't confess to all of them.

A month or so ago, the detective re-interviewed one of the frickers, and showed him pictures of my wife's jewelry and he said that the other two fricks had it and had stolen it from our house. He had no idea where it is now with one exception - he saw one of the fricks throw it into a canal. Did not say where or when.

So, these fricks live in a shitty place, with a canal right behind their apartment. I'm betting it's in there.

I have to get this ring back. It's a family heirloom that means a lot to my wife and that cannot be replaced. It's the only piece of jewelry we really care about (including engagement and wedding rings). Any suggestions?

I have access to a little no-power 10' flat I can float back there. Can I rent scuba gear and just go to town? (I've never dived, would I need to be certified to rent?) Y'all know of any schools or companies that might could do this, without spending a shitload of money? Anyone have any ideas? Is this the stupidest idea I've ever had? I know it's like looking for a needle in a haystack, but I gotta try.