This challenge was beaten with max difficulty without using exploits or glitches.

The challenge was to swim from Ebonheart to Solsheim from the very start of the game. You'd start off, take a silt strider and a boat to Ebonheart and swim. Unfortunately, you cannot do the challenge without purchasing some equipment, as you're too weak to fight off everything in the water until you reach Solstheim, nor can you outrun them.

So, the challenge was slightly modified. I allowed myself to loot everything in the Census & Excise office and, with the loot, purchase equipment from Arrille's tradehouse to make the challenge possible. Besides a dreugh that nearly killed me, I was able to fight off all the slaughterfish and thus make it to Solstheim and beat this challenge.