The interaction:
You say, 'What Deepwater harpoon?'
Weligon Steelherder says 'We do not award the Deepwater harpoon to just any paladin. Nobility is all well and good, but you must still prove yourself. We have heard rumors of a very distressing matter. Perhaps it is your calling. Are you ready to [prove allegiance to Erudin] and earn the Deepwater harpoon?'
for the quest
The Bridge isn't working.
The interactions before and after work fine, but there's no response from Weligon when asking about the Deepwater harpoon.