During which conflict did Lorthar of the Waves participate?
Here's what the lore says, drawn directly from the indexed sources:
-107 DR * During the Seventh Serôs War, the storm giant adventurer Lorthar of the Waves wields the once-lost Krakenscourge.
Source: -107 DR
-106 DR * The surprise return of the hidden triton race from the deep sea trench breaks the strength of Theocracy of the Deep Ones and the morkoths flee back into the deep, ending the Seventh Serôs War. The tritons assist in maintain the balance of power between the morkoths and shalarins in Serôs. * Lorthar of the Waves is killed in battle with an army of elite morkoth warriors in one of the last conflicts of the Seventh Serôs War. The Krakenscourge is taken by the Theocracy, but is quickly reclaimed by the tritons.
Source: -106 DR
-10800 DR * Cloaker Wars: The dwarven followers of Taark Shanat are attacked by the cloakers of Rringlor Noroth, and they fight over the caverns of Alatorin. The battle is won when Taark slays the four blue dragons who held the Rift of Dhalnadar. * Taark claims the dragons' lair and names it Brightaxe Hall, and creates the Wyrmskull Throne. From here, Taark forges the kingdom of Alatorin, marking the beginning of the First Great Age of Shanatar.
Source: -10800 DR
-1076 DR * The Orcgate Wars begin when the Orcgate is discovered by the orcs after five years of remaining dormant. Hundreds of thousands of them poured out and engulf northern Mulhorand and Unther. The Mulhorandi enlist Nar, Raumathari, Rashemi, and Sossrim mercenaries to aid them in the battle against the orcs.
Source: -1076 DR