Solo, hydrolock occurs when a liquid enters your cylinders. It could be any liquid but in this case it would be water. It could come in from a number of places but you should be concerned about the air intake. Internal combustion engines compress the contents of the cylinder and as liquids are not compressable, you can get all sorts of damage like broken pistons ...rods etc...
Google "Jeep snorkel"... one of the first entries will be a homemade snorkel that would work fine. I know that a lot of folks will say that you should be worried about the differential, transfer case etc. taking in water before the air breather but those other parts are usually sealed enough to make it through those creeks and rivers as long as you're not lingering in there too long.
Have a read...it's interesting....