Raleigh has plenty of water inside the beltline, but none of it is rideable. Lake Johnson, Lake Wheeler and Shelley Lake are municipal lakes with no personal watercraft allowed. The moment you cross to the north side of the city, that changes.
Falls Lake is the default choice for Raleigh riders. It begins at the Falls of the Neuse dam on the city's northern boundary and runs northwest toward Creedmoor, reachable from most of Raleigh via I-540, Falls of Neuse Road or Creedmoor Road. It is narrow and cove-heavy, which usually means calmer water.
Jordan Lake is the bigger ride. From downtown it means heading west on US 64 past Cary and Apex, so it is the longer trip for most of Wake County — but if your group wants genuinely open water, it is worth the extra time behind the wheel.
Both work well as a half-day plan out of Raleigh: ride in the morning while the water is flat, then be back in the city by lunch.