I once wiped out in La Jolla and my fish finder has not shown any adverse effects even though it spent a bit of time completely submerged

. However it is a basic fishfinder with less ports delicate equipment than many people use. Its a piranhamax 150. You could always disconnect it from the power and transducer and store it below deck if your yak has a front hatch (most malibus). If you leave it connected make sure the power and transducer ports are as plugged in as possible to prevent water from leaking in there.