Water

The solution for the speed that springs to mind would be to use one actor for the body of water, set it's image to a polygon and then adjust the physics accordingly by the points of the polygon. If the body of water splits, then it could form another actor that behaves the same way. A lot more complicated than the way you've done it, but if done properly it would be faster and probably more realistic!

Oooh! Fluid simulations! I had a working one a while ago, but i didn't upload it. I might refine it a bit and upload it later. As for speed, how are you determining the physics for a particle? For my physics, i had If it can fall, fall if it cant fall, move randomly to an open adjacent space.

mjrb4 : i will try ! :D Builderboy2005 : i determine my particle.. if there is a White Colored background, fall if there is a Blue Colored background, move to right (i think if random then it will be "shaking") If there is a Brown Colored at right, move to left

You should check out my scenario here http://greenfootgallery.org/scenarios/648 It uses single pixel actors, but in a unique and fast way It could also be expanded to incorporate multiple materials.