Summary
When an area_effect_cloud entity with a positive RadiusPerTick value is summoned near water, it will create bubble and splash particles when the area_effect_cloud grows in size and intersects with the water. This does not happen if the area_effect_cloud is summoned with it already intersecting the water.
Reproduction steps
Place water on the same Y level as the player, walk away a few blocks, then run the command:
/summon area_effect_cloud ~ ~ ~ {RadiusPerTick:1,Duration:10}
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Can confirm. This interestingly does not happen if the player is standing in the water:
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