Fill your bilge or the inside of the boat with water, it's the easiest way to find a leak. It may not be a rivet, might be a small hole or crack. If there's a way out, water will find it... and it won't take long! Once you've found the leak, then you can decide how you want to fix it. Loctite has a marine epoxy that works well and sets fairly quickly, you can find it at Wal-Mart.