My first instinct was to jump straight in. But with the depth sounder reading over 10m and no mask and no snorkel and no fins I figured my chances were pretty grim.
You need a different approach. Firstly, you find yourself some fellas who are willing to throw themselves into the river and go look for it.You will also need a boat and a rough idea of where the needle was dropped into the haystack. In my case I dropped it right next to a mooring. Handy! Then they dive down and have a look around while you guard the boat. There is no specific time for how long they should be down there. I feel it should be at least long enough to make a goggle mark round their face.
Time ticks by and your optimism starts to wane. Then, a circle water a few meters from the boat starts to fizz. Your scuba heroes emerge with......nothing! With a depth of 15.5m and a seabed like liquid dust you must resign yourself to the fact that your watch is gone. Accept that these things happen. Don't be mad at your scuba heroes because they didn't find it. Don't be mad at yourself for taking it off your wrist and putting it in your top pocket. Finding a needle in a haystack is hard. Let it go. It was just a watch. There's plenty more fish in the sea.