Lots of Civil War (and earlier) history was covered by Lake Wappapello. There is a Civil War camp site a couple of miles south of Old Greenville on US 67. A grave site of a CW soldier (Union I think) is located along the side of the highway near a spring.
New Greenville is only about 2 miles from the site of Old Greenville. Old Greenville is usually not flooded. The streets and building sites, including some foundations, are preserved. The Corps of Engineers has installed interpretive signage along the streets to show visitors what existed in Greenville before its unfortunate removal. Much history is lost by such projects. One interesting site, Davidson's Blue Spring is now submerged - divers call it Cannonball Spring for a CW cannonball found in the bottom of the rise pool. Local stories are that an entire cannon was dumped in the spring but I know nothing of the validity of that story.