Is swimming in the ocean challenging or frightening for people who have only swam in pools before?

Here in the Melbourne area, I've met a lot of people who moved here from inland regions where people only swim in pools before and many found swimming at the beach difficult because of all the wave actions.

I didn't grow up by the oceans but I did grow up in the great lakes region and in Lake Michigan the water is pretty turbulent too.

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So, I'm not sure how wave action feels to someone who hasn't experienced it.
Is swimming in the ocean challenging or frightening for people who have only swam in pools before?
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