All sorts of issues with this quest. Zott is just swimming in one spot, not following or anything.
Got it sorted in the end….
Restarted quest
listened to the entire movie (didn’t skip)
Zott jumped into water
Follow him immediately
Swim under the water enemies
Swim to Elli
Zott followed and revived Elli
Continued quest with no issues
Hope this helps others as Anet don’t seem to want to fix this one.