Hello Pitt,
I have a better understanding now of "in a square". You mean a photo frame.
There is a product available in modelrailroad scenery made by the company
Woodland scenics called Instant Water. The product reproduces the effect of
water very well. It is acrylic based so it is very safe to use.
First paint the base of your display the color that you would like to see through
and set it in the frame.
ex. brownish grey for a river bed or bluish green for ocean water.
Set whatever details you would like to see through your water.
ex. rocks, boulders, branches, sand etc.
Then pour in the liquid water in thin layers.
ex. 1cm layers and let dry......repeat.
After a few layers you should have an effect of depth. Obviously, there are
limitations. Set your model on the last layer and build up some acrylic gel
around the model to glue it to the base. Since this product will dry clear,
whatever is sitting on the bottom will show through.
To get an effect of waves you must work the acrylic when it is about 75% dry.
Touch up the crest of the waves with white paint to give white caps.
I hope this will be of help,
Have a nice day and happy modeling !
Joe