So, I've figured out how to create a 'lake' above the water line, i've even figured out how to make 'currents', but what I can't figure out, is how to get water to 'run' down a slope, so to speak.
I'm assuming I have to use some kind of animated-static/activator/ect to create the illusion of a river going down hill, but the only ones I have found, are those shallow-rocks with water rolling through them.

Would MrkKeepWaterfall01 do the trick?

You can make creeks and shallows by using the rocks with water rolling through them, and that's about it. You cannot make a slanted water body, if that's why you mean. If you need water to become lower, build a waterfall at a cell border, and have the water height lower. That's how they slowly transition from the high water levels above Falkreath, to the lower plains of Whiteruns. They step down with waterfalls. But there cannot be slanted water. (Only the aformentioned 'creek' pieces)

You can do sloped water with the activator water pieces. I actually prefer using these than setting a water level (in addition to the fact that water level is broken in interiors).

True but I'm not sure what issues would arrise with the water plane being slanted... Also water level in interiors has never worked, you're supposed to use placeable water inside. If your inside is too big for one of those, make it an exterior and fake it being an interior, like Blackreach.

Coming from Oblivion modding, water level is how you put water in interior cells there. I never really modded Fallout and obviously only just started Skyrim so I must admit it did confuse me for a while

I've done a test of slanted water planes and it seems to work correctly. However I'll need to take a further look, so use with caution

Wait, wait, wait. You guys pulled off adding water in an inside cell and figured out how to create a lake above the water line?

Please do share your knowledge. Been wondering how to do this for ages.

You can modify water cell height in exteriors by going into cell properties. This doesn't work in interior cells however.
If you want to add bodies of water, search for Waterxxxx activators. You place and scale them like any other plane.

But how'd you make a lake above ground without making the cell look awful, with a square plane of water just floating?
Example: Clearspring Tarn

By placing a water activator plane, and then modifying the landscape around it to mask the edges of the plane, or use statics such as rocks.

luckilly for me, my lake is large enough, I can adjust the landscape around it to 'fit' the square areas...
The hard part is goign to be the 'river' part imo. its not nearly as 'wide' as a whole cell, so... its either use activators or water levels.
I may use the waterfall step method... depending.

I'll check out that mrkeepwaterfall01 out, http://www.gamesas.com/user/784925-orcman00/ to see if that does it.
this island is going to have a few unique things about it, and having a 'lake' at a high point and rivers flowing outwards into the sea, is one of those thigns I'd like to do. I may end up, reducing the total hieght of the 'lake' to make it more gradual, and natural.

I'd perfer to make the island in the world hieght editor part, but thats just... borked.