Not sure what it's called in ESO but I'm referring to the mechanic Zeinmax uses to prevent you swimming 'off the map', Blizzard use the term 'fatigue'.

It's far too brutal and usually leads to death within seconds. For example I was just swimming around the coast and suddenly I start taking massive damage, I don't even have time to realise what's happening and turn back before I'm dead.

Same this happened trying to swim from an ice floe only yards off-shore.

Please, at least make the damage less per unit time or else ramp it up, or give a warning. It really sucks to die 5 seconds after swimming into an area that isn't even visually different; at least is WOW the water colour is a visual clue you're about to enter a 'fatigue' zone.