The water on Riven has unique curious properties. It seems to have an aversion to heat that can act as semi-solid, from opening pocets of air to neglecting gravity.
Gehn performed experiments to study the water. He had some water enclosed inside a closed glass bubble mounted on a portable stove. Gehn and/or the Rivenese also employed these properties for underwater transportation.
He speculated that a life form that resides in it - a type of bacteria or other motile unicellular organism, that has a special structure capable of holding bits of water. These organisms appear sensitive to heat, and their combined dramatic aversion to heat sources (possibly via surface tension or a stronger force) causes the effect of the composite body of water to move accordingly. The aversion to heat is possibly explained by the organism's vulnerability to it; indeed, extended boiling or other prolonged exposure to extreme heat seems to kill them. Due to other pressing matters he abandoned his experiments and didn't confirm the nature of this phenomenon.