Not a unique thought by the looks but the one time I have seen a shark in the Swan River. Saw it thrashing around in about chest deep water. Not sure what it had. I sailed past about 30 meters upwind of it and on for 50m gybed and gave it another sail by, sure by this time what I was seeing as often the dolphins are in the shallows doing almost the same thing.
Sailed across the river and on the way back my eyes were peeled searching for any sign. As I got near the area had to gybe and with the thought that it was about here and no sign of it, my head was singing the mantra "don't fall in, DON"T FALL IN". Craved downwind nicely and as I went for the foot change front foot stuck in strap and in I went.

Have never scrambled back onto my board as quickly as that but the brief seconds I was in the water standing chest deep was complete horror.
Now I nearly always remember to loosen my feet in the straps before gybing.

Nearly.