Is it legal to spearfish the area? That would justify you snorkling/scuba diving and repeatedly being under water. (Nevermind if fish are few, not everyone knows you know fish.)
Short of being allowed to spearfish , a fishing rod can hint that you are fishing. That won't fool binoculars though...
You should never drop your knife in the water. But if it's a sentimental one , going swimming to freedive and try to recover it makes sense.
Too bad the yak was moving when you dropped it over there.. No wait , it was upwind further. No , you spotted a big rock on the way by after you dropped it. Crap , it must have drifted on the fall.
Might as well try a crude grid if you have time before you leave. And note the area's coordinates and landmarks if you don't find it so you can return to look for it again.
Dang it. Carried that knife after it was gifted for a very long time....
Ya know, RC?
For some reason that reminds me of a trip of my own.
I'd decided to try water hunting again. I made the equipment necessary and thought I'd try them out in a nearby creek. This creek ran thru a state park though. (Something I didn't know at the time).
Anyway, I waded downstream and into the confines of the park. Happily cleaning up a plethora of junk! The equipment was working! I didn't expect to find gold doubloons!
Along comes this young park ranger, jumping up and down on the shore and ordering me out of the creek! Can't do that here! Park doesn't allow! There's a fine! Etc. Etc.
I wandered over to him, staying in the creek. In short order, his backup arrived which he must've radioed for...to handle this invasion/destruction of park property!!
The elder, calmer park ranger supervisor asked me if I'd found much. I showed him my trash bag and a lone button. He smiled, then turned to the younger, Gestapo wannabe and asked what the problem was here. He started trying to quote park regulations, fines, etc. The older man put his hand on his shoulder to stop him. Then explained.
"One...this man is *not* on park property!
Two...the land under the creek is *not* part of the park!
Three...you've been *very* rude in dealing with this person who pays our salary!
Four...This man is doing nothing wrong and is even cleaning up the creek!
Five....Apologize to this man and then go study your own rules and regulations some more!"
The supervisor and I chatted a bit more about past finds, shook hands and parted.
For some reason, I smiled the rest of the day, despite no "good" finds.