I noticed how it's impossible to get out of the water if there are 2 streams of water on both sides of it.
italso work with lava.

if you have 2 source water block at a distance of 2 block eachothers dig into an open canal in the ground and you fell into it, you can easily escape from it by pressing the spacebar and get out, in every blocks of it.

but if we add 2 stream of water on each side, (we can leave the source water block or delete it, it won't affect it ) suddently we cant jump out anymore, of course unless we use the stream do swim up.

I also tried a cross pattern, if the central water block made by the intersection of the 4 is still water you can escape it, if I put a bloc on it then you can't escape from the stream on the canals arms

I've tried this with different distances and shapes on my video.
also I'm attaching a gallery of my test setup so you can replicate the effect of it.

Gallery of pictures: http://imgur.com/a/M3CQR
I made a video to explain it better: http://youtu.be/sSAXz1tZNUo