Start by opening an image of the a dolphin
Create selection of the fish using polygon lasso tool. Press Ctrl+J to duplicate the selection in a new layer.
Hide the duplicate layer. Clone the water area to hide the dolphin in original layer.
Similarly create selection of the water splash. Duplicate the selection in a new layer.
Hide the layer and clone original layer.
Duplicate the water layer. From filter menu select distort>>ripple. Apply settings as shown.
Create a few duplicate of the dolphin layer. Move and place each duplicate layer to show the diving motion.
You may have to rotate the dolphin layer.
For one duplicate erase most of the dolphin layer keeping only it's tail to visible.
For the next duplicate reduce the visibility of the dolphin layer as if the dolphin is under water.
Unhide the splash layer and place it over the point where dolphin just hit the water.
Click add vector mask form the layer palette.
Create a rectangular selection using rectangular marquee tool.
Press Ctrl+Alt+D to feather the selection.
Fill with black color. Unlink the layer content and layer mask thumbnail.
Open animation window. For the first frame keep the dolphin layer visible that is barely visible from the right edge.
Duplicate frame and keep unhiding the next dolphin layers.
For the third frame move the splash mask halfway upwards.
Duplicate frame shift the mask completely upwards to show the full splash.
Duplicate frame. Start unhiding the underwater dolphin layer.
Duplicate frame. Move the splash mask downwards to hide the splash completely.
Duplicate frame. Move the fish to the left edge.
Press Ctrl+Alt+Shift+S to save an optimized animated GIF.
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