Speak with Explorer Fellhew.
Prospector Ironband is heading an excavation of ancient ruins east of the lake. His progress has been slow lately, especially considering all the supplies we've sent him.
Ironband's a stout, honest dwarf who values results, which has me worried that forces are at work against him.
Go to Ironband's Excavation and speak with Magmar Fellhew. He manages the details of the site and will know why there's a slowdown.
To get to the excavation site, go around the southern tip of the lake, then head east.