Yup! In Fantasmic on either coast, the gas comes out of a multitude of pipes below the water which then floats to the top since its denser.
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You can barely make out the gas lines in the WDW birds eye pic, but it’s pretty much the same in DL.
I’m sure it’s doable for the AK lake, it’s just a matter of costs and maintenance. Can the lake be easily drained and accessed when needed/for maintenance? Or would they need to create a rising platform type thing, similar to WoC.