Well, I don't know how realistic it is...but here's something you can look at...maybe it will give you some ideas
http://scratch.mit.edu/projects/Paddle2See/506747
By the way, this isn't so much a suggestion as a question about Scratch...so I'll move it over to the All About Scratch forum
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What game was it? Because it really depends. You might be able to just use the sprite they used.
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Try drawing some lines in the water, and having the lines move accordingly to the water flow.
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