Sharp edges or triangles at beach edge? How do I smooth them out?

Could you please help me smooth out this orange line. I think that is why the edge of my beach is not straight and looks strange. Thank you:)

Doubt you can.
You have around 1 vert per meter.
Triangles on curves are inevitable in this (or any landscape curve) scenario.

Only way you’d be able to do something is to create a dedicated edge mesh that has more definition and gets merged back into the sand.

That said. I don’t think you have a need for it if the edge water is so transparent.
Without the line you really shouldn’t see much of anytning…

So show us what the problem you have is in a screenshot - maybe there are other solutions.