Step 1
First: open illustrator and set the dimensions of a new document to
fit your screen. My screen dimensions are 1920 x 1200 px so this is what
I set my document to. Fill the background with black.
Now, create several radial gradients similar to the image below. Re-size
and move toward the middle of the document and positioning them to
express light from above and reflecting off the bottom. Set the
transparency of each gradient to screen.
Adjust them until you get something like this.
It doesn't need to be perfect, you can always move them around later.
Step 2
Now for the fun part. Create a rectangle about 50px high and around 500px wide using bright colored gradient.

Duplicate the rectangle several times and change the transparency on a few inpidual rectangles to overlay, soft-light and hard-light. Align them horizontally and then use the transform each option.

Go to Object -> Transform each and mess around a bit until you get a "forced randomness" LOL
Something like this will be fine.
Step 3
Now bust out your handy dandy Pucker Tool and mess around with it. Run through, drag and pull on the gradients until you get an esthetically pleasing abstraction. This is how I adjusted my Pucker Tool. It's O.K. to laugh.
After all that puckering around, you should have something like this, or at least close to it.
O.K. now we are going to make another one; but, solid black for this one and a little bit bigger. We are going to use this one behind the gradated piece to show depth.
Place them in the document and adjust until they look good to you.
Step 4
O.K. now for the bottom of the sea. A bunch o' seaweed or lost city,
which ever you prefer. I prefer the lost city so thats what we are going
to make now.
To make a city we just throw in a bunch of rectangular shapes along a
horizontal path like so.
And continue until we have something like this, and then we just unite the object using the pathfinder tool.
Now we will add some character and degradation to the watered city by using the Scallop and and Wrinkle Tools.
Now just run the Wrinkle tool above the city.
And pull out the Scallop Tool and use these adjustments.
And you should have something like this, or not.
Now place your city at the bottom of the sea.
Step 5
Next up...bubbles. Make a few different sized circles, fill with black and place them randomly and lower the opacity to about 40%. We have to turn these into a scatter brush so take your new circles and drop them into the brush palette and set the scatter brush options as shown below.
Take your new bubbles brush a draw out 4 groups of bubbles, 2 groups need to be white to balance out the darker ones for depth.
Add one set to the top and the other to the bottom of your sea giving you a pretty nice look.
Step 6
We need some fish, so we are going to Warp one out of a circle, just because we can.
Go get yourself a circle and set your warp tool Scotty.
This is our fish, well not yet, but it can be. Start by dragging the warp tool from inside the circle outwards and shape the tail until it's recognized as one.
keep going.
Almost.
Now we have to adjust the Warp Tool a little and finish him off.
If your crazy enough to do this, than it should look like this.
I wouldn't really recommend doing it this way if your not use
to the Warp Tool, You can easily use the pen tool. Now duplicate the
fish, flip horizontally and adjust the opacity on one of them for some
depth again.
After placing your fish and positioning them until you are happy you may
want to add some seaweed to your city or submarines, whatever you like,
just have fun.

