Any time you sail to new places, especially in search of new biomes, or across the water to new lands, it always a good idea to bring along materials to build a PORTAL, while also having a spare portal set up at home, so that, as soon as you arrive in the new place, you can set up that portal and have a connection to either get home quickly or get back to your gear if you happen to die.

It should also be mentioned that you should be geared up and fully PREPARED for each new biome you travel to. Each biome, in the progression, has specific resources and items, that must be gathered, crafted and obtained, to help you gear up for the next biome, and if you try to skip past that progression, Valheim will kill you dead in an instant.

Before you travel to the swamps you should have poison resist mead, bronze gear and able to craft portals, at bare minimum.