"Yeah, the reactivity I have in mind will activate if they touch the circle, so enough water for them to swim close and put a hand on it will do. And there can be a watermage or maybe just a spell to make hovering water on the Elcenian end, and a canal, and we make sure they line up, and they can get into the ocean from there, and maybe if they live in the opposite corner of the world they have a bit of a trip but at least they aren't drowning. Size I'm thinking they'd need maybe ten percent of its area in a blob near an edge."