I'm not sure you need the "part" in there. Look at Push of the Gentle Wave. The target is individual, and the basic idea is pretty similar (calm but forceful motion, oriented on an object for the duration, which in this case is a boat). The only reason that spell seems to need voice range is that you can't always reach the water behind a boat from a boat. If you were willing to stick to rowboats or willing to dangle from a rope or something you could probably make a touch version of the spell.
Push of the Gentle Wave seems to use an "individual" quantity of water that is more like the Auram definition of "individual", ie a volume of water near the casting point, rather than a whole lake or ocean.
"Individual: a stretch of water with the same composition and curent. A small pond, part of a stream, or a spring.". We would use the first definition, not the second.
What Push of the Gentle Wave does is define "the water around the boat" to have that composition and current. The fact that the current is set by the rego spell or the fact that the water could be a pond or an ocean is irrelevant, the spell itself has now set up a defined aquam individual as a result of casting the spell.
Unlike push of the gentle wave, upwellings forceful enough to support something as heavy as a human aren't real common in nature, so the unnatural+1 probably has to stay.
Lets see where that puts us
Base effect5 (forceful but gentle=4, +1 touch, +0 individual)
reaq10 Gift of the Crocodile's Legs (diameter) - you can run at full speed over any mud that is not so deep that it would completely prevent normal (non-swimming) movement without the spell (a crocodile can charge over mud just as fast as it can over dry land, if not faster. The rego just holds the mud together long enough to support you without sinking where your feet are)
reaq10 Gift of the Floating Wood (diameter) - this spell will allow you to float on the surface of the water, preventing sinking, but you are still at the mercy of waves and current, and must swim (rather than stand/run) to move in any way other than bobbing like a cork.
reaq10 Push of the Friendly Wave (concentrate) - touch version of Push of the Gentle Wave, this could allow you to swim faster or could complement gift of the floating wood to let you mitigate current. It wouldn't help a bad swimmer stay afloat, but you're probably fine with a minimal swim check (maybe encumbrance+swim+strength>0) just to keep your head above water and let the wave carry you.
reaq10 Skip the Stone (unnatural+1, momentary) - you can run for one round over water. If you stop moving, you will sink. Fastcasting is required to stay above the water for longer distances. This spell doesn't help if you are already immersed in water.
reaq15 Water Walk ( unnatural+1,diameter) - for the duration of the spell you can stand/walk/sit/lie on water with no ill effects. If cast while immersed in water, you are pushed out of the water.
reaq15 Neptune's Gift (complex effect+1, concentration) - You don't sink no matter how bad you are at swimming, and a friendly wave/current takes you in a direction you want to go. The direction is set at time of spellcasting, a single large wave carries you until it breaks on a shore or you stop concentrating.